Symmetrix Foundations Student Resource Guide

Copyright © 2004 EMC Corporation. All Rights Reserved.

Symmetrix Foundations, 1

11

EMC Global Education© 2004 EMC Corporation. All rights reserved. These materials may not be copied without EMC's written consent.

Symmetrix Foundations

Welcome to Symmetrix Foundations. EMC offers a full range of storage platforms, from the CLARiiON CX200 at the low end to the unsurpassed DMX3000 at the high end. This training provides an architectural introduction to the Symmetrix family of products. The focus will be on DMX, but prior generations of Symmetrix will also be discussed.

Copyright © 2004 EMC Corporation. All rights reserved.These materials may not be copied without EMC's written consent.EMC believes the information in this publication is accurate as of its publication date. The information is subject to change without notice. THE INFORMATION IN THIS PUBLICATION IS PROVIDED “AS IS.” EMC CORPORATION MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WITH RESPECT TO THE INFORMATION IN THIS PUBLICATION, AND SPECIFICALLY DISCLAIMS IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Use, copying, and distribution of any EMC software described in this publication requires an applicable software license.



EMC Global Education© 2004 EMC Corporation. All rights reserved. 22

Audio Portion of this Course

The AUDIO portion of this course is supplemental to the material and is not a replacement for the student notes accompanying this course.EMC recommends downloading the Student Resource Guide (from the Supporting Materials tab) and reading the notes in their entirety.

The AUDIO portion of this course is supplemental to the material and is not a replacement for the student notes accompanying this course.EMC recommends downloading the Student Resource Guide from the Supporting Materials tab, and reading the notes in their entirety.




EMC Technology Foundations

EMC Technology Foundations (ETF) is a curriculum that presents overviews of EMC products and technologies including:– Symmetrix and CLARiiON Storage Platforms and Software– SAN, NAS and CAS Networked Storage Solutions – Advanced storage management software

The EMC Technology portfolio consists of end-to-end services and platforms designed to accelerate the implementation of Information Lifecycle Management (ILM)ILM uses EMC technologies to enable organizations to better, and more cost-effectively, manage and protect their data, and achieve regulatory compliance. It improves the availability of their business information in a way that connects its use to business goals and service levelsThis course represents one part of the ETF curriculum

Companies across all industries are constantly launching new business-critical applications turning information into strategic corporate assets. Value to the bottom line for customers, suppliers, and partners is often directly related to how easily this information can be shared across the enterprise and beyond.

Information Lifecycle Management (ILM) is a flexible information-centric strategy that includes automating the process of connecting applications and servers in an organization to its company’s information. ILM includes Direct Attached Storage (DAS), Storage Area Network (SAN), Network Attached Storage (NAS), Content Addressed Storage (CAS), and software for management and automated provisioning.

ILM facilitates the integration of SAN and NAS, extends the reach of enterprise storage, and delivers a common way to manage, share, and protect information. It also takes advantage of today’s network and channel technologies to consolidate servers and storage, centralize backup, and manage the explosive growth of data.




Symmetrix Foundations

After completing this course, you will be able to:Describe the basic architecture of a Symmetrix Integrated Cached Disk Array (ICDA)Identify the front-end, back-end, cache, and physical drive configurations of various Symmetrix modelsExplain how Symmetrix functionally handles I/O requests from the host environmentIllustrate the relationship between Symmetrix physical disk drives and Symmetrix Logical VolumesIdentify the media protection options available on the Symmetrix

These are the learning objectives for this training. Please take a moment to read them.




Symmetrix Integrated Cached Disk Array

Highest level of performance and availability in the industryConsolidation– Capacities to Terabytes– Vast host connectivity– SAN or NAS

Advanced functionality– Parallel processing

architecture– Intelligent prefetch– Auto cache destage– Dynamic mirror service policy– Multi-region internal memory– Predictive failure analysis and

call home– Back-end optimization

Enginuity Operating Environment– Base services for data

integrity, optimization, security, and Quality of Service

– Core services for data mobility, sharing, repurposing, and recovery

There are basically three categories of storage architectures: Cache Centric, Storage Processor centric, and JBOD (Just a Bunch Of Disks). The Symmetrix falls under the category of cache centric storage and is an Integrated Caching Disk Array.




Enginuity Operating EnvironmentEnginuity Operating Environment is the Symmetrix software that:– Manages all operations– Ensures data integrity– Optimizes performance

Enginuity is often referred to as “the microcode”Solutions Enabler provides common API and CLI interface for managing Symmetrix and the entire storage infrastructure

EMC and ISV develop management software supporting heterogeneous platforms using Solutions Enabler API and CLIs

Symmetrix Hardware

Enginuity Operating Environment

Solutions Enabler Management

Symmetrix Based ApplicationsHost Based Management Software

ISV Software

Before we get into the hardware, let’s briefly introduce the software components, as most functionality is based in software and supported by the hardware. Enginuity is the operating environment for the Symmetrix storage systems. Enginuity manages all Symmetrix operations, from monitoring and optimizing internal data flow, to ensuring the fastest response to the user’s requests for information, to protecting and replicating data. Enginuity is often referred to as “the Microcode”. Solutions Enabler is storage management that provides a common access mechanism for managing multivendor environments, including the Symmetrix, storage, switches, and host storage resources. It enables the creation of powerful storage management applications that don’t have to understand the management details of each piece within an EMC user’s environment. Solutions Enabler is a development initiative (that is, a program available to Integrated Software Vendors (ISVs) and developers through the EMC Developers Program™) and provides a set of storage application programming interfaces (APIs) that shield the management applications from the details beneath. It provides a common set of interfaces to manage all aspects of storage. With Solutions Enabler providing building blocks for integrating layered software applications, ISVs and third-party software developers (through the EMC Developers Program), and EMC software developers are given wide-scale access to Enginuity functionality.




Symmetrix Card Cage

4896384576288288144144120

Maximum Disk Drives

32GB2228230

128GB 444DMX1000P

64GB4448530

64GB4888830

256GB 888DMX 3000

256GB 888DMX2000P

256GB 8412DMX2000

128GB 426DMX1000

64GB 222DMX800

Maximum Cache

Maximum Cache Directors

Maximum Back End Directors

Maximum Front End Directors

Model

DMX3000DMX2000DMX1000DMX800

Though we logically divide the architecture of the Symmetrix into Front End, Back End, and Shared Global Memory, physically, these director and memory cards reside side-by-side within the card cage of the Symmetrix. The DMX “P” model is configured for maximum performance rather than connectivity.




DMX2000

Symmetrix Architecture is based on the concept of N + 1 redundancy (one more component than is necessary for operation).Continuous Operation even if failures occur to any major component:

• Global Memory Director boards • Environmental Control Card• Channel Director boards • Cooling Fan Modules• Disk Director boards • Power modules• Disk drives • Batteries• Communications Control Card • Service Processor

Power Subsystem: The Symmetrix has a modular power subsystem featuring a redundant architecture that facilitates field replacement without interruption. The Symmetrix power subsystem connects to two dedicated or isolated AC power lines. If AC power fails on one AC line, the power subsystem automatically switches to the other AC line. System Battery Backup: The Symmetrix backup battery subsystem maintains power to the entire system if AC power is lost. The backup battery subsystem allows Symmetrix to remain online to the host system for one to three minutes (set in IMPL.bin file) in the event of an AC power loss, allowing the directors to flush cache write data to the disk devices. Symmetrix continually recharges the battery subsystem whenever it is under AC power. When a power failure occurs, power switches immediately to the backup battery, and Symmetrix continues to operate normally. When the battery timer window elapses, Symmetrix presents a busy status to prevent the attached hosts from initiating any new I/O. The Symmetrix destages any write data still in cache to disk, spins down the disk devices, and retracts the heads and powers down.Symmetrix Emergency Power Off: The Symmetrix emergency power off sequence allows 20 seconds to destage pending write data. When the EPO switch is set to off, Symmetrix immediately switches to battery backup, and initiates writes of cache data. Data is written to the first available spare area on any devices available for write. The director records that there are pending write operations to complete, and stores the location of all data that has been temporarily redirected. When power is restored, all data is written to its proper volumes.




Cache Management

Data path through Symmetrix Data destaged from cache

There are three functional areas:• Global Memory - provides cache memory and link between independent front end and back end • Channel director - how the Symmetrix connects to the host (server) environment (multi-processor circuit

boards)• Disk director- how the Symmetrix controls and manages its physical disk drives, referred to as Disk Directors or

Disk Adapters

Channel directors handle I/O request from the host, while disk directors manage access to disk drives. The channel directors and disk directors share global memory. Cache is used for staging and destaging data between the host and the disk drives. Data is stored in cache as write pending, and an acknowledgement of data receipt is returned to the host. The disk directors will write the data from cache to disk at a later time. The cache directory contains information on data location, which data is still in cache, and which data has been written to disk.




Direct Matrix Architecture

What differentiates the Symmetrix generations and models is the number, type, and speed of the various processors, and the technology used to interconnect the front-end and back-end with cache.

The DMX Series system currently uses M5 memory boards. Each memory board has sixteen ports, one to each director. Each region can sustain a data rate of 500MBs, 4 regions per card, so 2GB per card. If a director is removed from a system, the usable bandwidth is not reduced. If a memory board is removed, the usable bandwidth is dropped by 2GB/s. In addition to 8 ports to front end hosts, or backend disks (depending on board type), each director also has 8 ports to memory, one to each of the memory boards. All four processors can connect concurrently to four different memory boards. In a fully configured Symmetrix DMX2000/3000 system, each of the eight director ports on the sixteen directors connects to one of the sixteen memory ports on each of the eight global memory directors. These 128 individual point-to-point connections facilitate up to 128 concurrent global memory operations in the system.




Symmetrix DMX Architecture

Separate Control and

Communications Message Matrix

Disks

Servers

Another major performance improvement with the DMX is the separate control and communications matrix that enables communication between the directors, without consuming cache bandwidth. This becomes more apparent as we talk about read and write operations and the information flow through the Symmetrix later in this training.




DMX Director Pairing

Directors are paired Processor to Processor using the 17 rule. This means mirrors will not be placed across Directors using the 17 rule (unless only 2 Directors are present). Paired directors provide redundant paths to dual ported disks, and will not use the same Port Bypass Card (PBC) in order to maintain redundancy on the Port Bypass Card level. The PBC acts as the hub for all the Fibre disk drives in the disk cage.




DMX: Dual-ported Disk and Redundant Directors Directors are always configured in pairs to facilitate secondary paths to drivesEach disk module has two fully independent Fibre Channel portsDrive port connects to the Director by a separate loop– Each port connects to different

Directors in the Director pair – Port bypass cards prevent a

Director failure or replacement from affecting the other drives on the loop

Directors have four primary loops for normal drive communication and four secondary loops to provide alternate path if the other director fails (based on performance models)

Disk Director 1 Disk Director 16

P

S

P

S

P

S

P

S

S

P

S

P

S

P

S

P

P = Primary Connection to DriveS= Secondary Connection for Redundancy

Symmetrix DMX back-end employs an arbitrated loop design and dual-ported disk drives. Here is an example of a 9 disk per loop configuration. Each drive connects to two Disk Directors through separate Fibre Channel loops. The loops are configured in a star-hub topology with gated hub ports and bypass switches, that allow individual Fibre Channel disk drives to be dynamically inserted or removed.




Back-end Director Pairing 9-drive loopDirector 1d

dA

c

b

aBA

BA

B

AB

BB

AA

BB

AA

BB

d A

c

b

a A

BA

B

AB

BB

AA

B

AA

Director 16d

16dC0

1dC1

16dC2

1dC3

16dC4

1dC5

16dC6

1dC7

16dC8

PBC

PBC

Legend

Primary Connection Director 1d

Bypass Connection Director 1d

Primary Connection Director 16d

Bypass Connection Director 16d

The Port Bypass Card contains the switch elements and control functions to allow intelligent management of the two FC-AL loops embedded in each disk cage midplane. There are two Port Bypass Cards per disk cage midplane. Each disk cage midplane can support 36 FC drives.

Each Processor has two ports, each with devices in the Front, as well as in the Back, Disk Midplane. In the above slide, we are showing only one port from Director 1d, and one port from Director 16d. Notice that each Director has the potential to access all Drives in the loop (9-drive loop configuration in this example). Notice also that using the Port Bypass Card, each director is currently accessing only a portion of the drives (Director 1d has 4 Drives; Director 16d has 5 Drives).

These Directors will have an opposite configuration on their second port, which is connected to a different Port Bypass Card and Disk Midplane. For example, Director 1d has 4 Drives in this Disk Midplane, and on its other port it will have 5. Director 16d has 5 Drives in this Disk Midplane, and on its other port it will have 4. Director 1d and Director 16d will be paired in both the front and back Disk Midplanes (only one shown here). With no component failure, each processor will manage 4 drives on one port and 5 Drives on the other. These reside in Front and Back Disk Midplanes and are referred to as C and D Devices. If the processor on Director 1d fails, the processor on Director 16d will now access all 9 Drives on this loop.




DMX800 Architectural Overview

SPE Enclosure

The physical layout of the DMX800 is very different than previous Symmetrix models. Directors, Memory, back adapter functionality, communications and environmental functions are all in the Storage Processor Enclosure (SPE). The DMX800 looks similar to the CLARiiON CX600 series and does in fact use the same back end style components.

The SPE Contains 2 - 4 Fibre director boards, up to 2 Multi Protocol Boards, 2 Memory boards, 2 Front-end Back-end (FEBE) adapters, Redundant Power Supplies and Fan module.

The DMX800 does not contain disk drive cages; drives are in a separate Disk Array Enclosure (DAE). Each DAE has 2 Link Controller Cards (LCCs) and 2 Power Supplies. The Service Processor is replaced by a 1U (1U = 1.75”) Server, the Server will support 4 SPEs via 4 of its 6 Ethernet connections.

Batteries, or Standby Power Supplies (SPS), are in a separate 1U enclosure. Each SPS enclosure contains two SPSes, and supports either two DAEs or one SPE. There are no ECM or CCM boards in the DMX800. The Communication and Environmental functions are taken care of by Directors and FEBE Adapters.




Symmetrix 5.X LVD Architecture

80 MBS SCSI LVD Bus

Shared Global Memory Back EndFront End

Channel Director

Processor bPowerPC 750

333Mhz

Low Memory

Top High

Bottom Low Bottom High

Processor aPowerPC 750

333 Mhz

400 MBS Internal

Bus

400 MBS Internal

Bus

Top Low

High Memory

Cache

Disk Director

Processor bPowerPC 750

333Mhz

Processor aPowerPC 750

333 Mhz

8230½ Bay Cabinet

8530

8830

1 Bay Cabinet

3 Bay Cabinet

Here is another example of the MOSAIC 2000 Architecture. This is the basic architecture for Symmetrix 5.X LVD: • Bus speed of 400MB/s for an aggregate of 1600 MB/s• Back End Directors and Drives support Ultra 2 SCSI LVD (Low Voltage Differential) and the bus speed of 80

MB/s• The director processors are now 333 Mhz; ESCON directors are 400 Mhz• Each director connects to 2 internal system buses (Top High & Bottom Low for odd directors | Bottom High &

Top Low for even directors )• M4 Generation of Memory Boards support LVD ( Low Voltage Differential or Ultra 2 SCSI Enginuity 5567 or

greater)

The Symmetrix 5 (8730, 8430) follows the same bus structure but has speeds of 360MB/s for an aggregate of 1440 MB/s.

The Symmetrix 4.X family is based on a dual system bus design. Each director is connected to either the X bus (odd numbered director) or Y bus (even numbered director). Each director card has two sides, the b processor (top half) and the a processor (bottom half). Data is transferred throughout the Symmetrix (from Channel Director to Memory to Disk Director) in a serial fashion along the system buses. For every 64 bits of data, the Symmetrix creates a 72 bit “Memory Word” (64 bits of data + 8 bits of parity). These Memory Words are then sent in a serial fashion across the internal buses to director from cache or to cache from director.




DA 2

Processor b

MIDPLANE

DA 1

Processor b

MIDPLANE

Port D

Port C

Port D

Port C

Solid line = Primary PathDotted line = Secondary Path

Symm 5: Dual-Initiator Disk DirectorDisk Directors are installed in pairs to facilitate secondary paths to drivesIn the unlikely event of a disk director processor failure, the adjacent director will continue servicing the attached drives through secondary path– In this example, DA1

processor “b” would see ports C & D for DA2 processor “b” as its A & B ports in a fail-over scenario

Protecting against DA processor card failurePhysical drives are not dual-ported but are connected via a dual-initiator SCSI BusVolumes are typically mirrored across directors

Symmetrix 4 and 5 architectures utilize a dual-initiator back-end architecture that ensures continuous availability of data in the unlikely event of a Disk Director failure. This feature works by having two disk directors shadow the function of each other. That is, each disk director has the capability of servicing any or all of the disk devices of the disk director it is paired with. Under normal conditions, each disk director only services its disk devices. If Symmetrix detects a disk director hardware failure, Symmetrix “calls home” but continues to read from or write to the disk devices through the disk director it is paired with. When the source of the failure is corrected, Symmetrix returns the I/O servicing of the two disk directors to their normal state. Prior to the Symmetrix DMX, mirrored volumes were configured with what is known as the “rule of 17”. Because of where within the card cage the DA pairs reside (1/2, 3/4, 13/14, 15/16), as long as the sum of the DA director numbers equals 17 (1/16, 2/15, 3/14, 4/13), the mirrors will always be on different internal system buses and dual initiators for the highest availability and maximum Symmetrix resources. Note: On the 4.x family, dual-initiation occurs by physically connecting one disk director’s port card to the port card of the adjacent disk director with a dual slotted adapter card.




Symmetrix Back End

Symmetrix 4 and 5 architectures use 40/80MB/s SCSI to connect physical drives with a maximum of 12 drives per portDAs installed in pairs on adjacent slots within the card cage of Symmetrix DMX Architecture uses 2Gb Fibre Channel drives– Eight ports per Director – Maximum 18 dual ported

drives per port

Port C

Port D

Port C

Port D

Disk Director

Processor b

Processor a

d A

c

b

a BABA

BAB

BB

AA

BB

AA

The primary purpose of the Back End director is to read and write data to the physical disks. However, when it is not staging data in cache or destaging data to disk, the disk director is responsible for proactive monitoring of physical drives and cache memory. This is referred to as disk and cache “scrubbing”.

“Disk Scrubbing” or Disk Error Correction and Error Verification: The disk directors use idle time to read data and check the polynomial correction bits for validity. If a disk read error occurs, the disk director reads all data on that track to Symmetrix cache memory. The disk director writes several worst case patterns to that track searching for media errors. When the test completes, the disk director rewrites the data from cache to the disk device, verifying the write operation. The disk microprocessor maps around any bad block (or blocks) detected during the worst case write operation, thus skipping defects in the media. When the internal soft error threshold is reached, the Symmetrix service processor automatically dials the EMC Customer Support Center and notifies the host system of errors via sense data. “Cache Scrubbing” or Cache Error Correction and Error Verification: The disk directors use idle time to periodically read cache, correct errors, and write the corrected data back to cache. This process is called “error verification or scrubbing.” When the directors detect an uncorrectable error in cache, Symmetrix reads the data from disk and takes the defective cache memory block offline until an EMC Customer Engineer can repair it. Error verification maximizes data availability by significantly reducing the probability of encountering an uncorrectable error by preventing bit errors from accumulating in cache.




Symmetrix Global Cache Directors

Memory boards are now referred to as Global Cache Directors and contain global shared memoryBoards are comprised of memory chips and divided into four addressable regionsSymmetrix has a minimum of 2 memory boards and a maximum of 8. Generally installed in pairsIndividual cache directors are available in 2 GB, 4 GB, 8 GB, 16 GB and 32 GB sizesMemory boards are FRUs and “hot swappable” (does not require Symmetrix power down or “reboot”)

Cache boards are designed for each family of Symmetrix. Symmetrix 4.8 uses the M2 generation of memory boards that connect to both the X and Y internal buses. Symmetrix 5 uses the M3/M4 generation of memory boards and the DMX uses M5. Because these boards have different designs, they cannot be swapped between families of Symmetrix. On Symmetrix 5, memory boards that connect to the Top High and Bottom High internal system buses are referred to as “High Memory”. Conversely, boards that connect to Top Low and Bottom Low are known as “Low Memory”.

DMX uses direct connections between directors and cache.When configuring cache for the Symmetrix DMX systems, follow these guidelines:

• A minimum of four and a maximum of eight cache director boards is required for the DMX2000 and DMX3000 system configuration; and a minimum of two and a maximum of four cache director boards is required for the DMX1000 system configuration.

• Two-board cache director configurations require boards of equal size.• Cache directors can be added one at a time to configurations of two boards and greater.• A maximum of two different cache director sizes is supported, and the smallest cache director must be at least

one-half the size of the largest cache director.• In cache director configurations with more than two boards, no more than one half of the boards can be smaller

than the largest cache director.




Cache Age Link Chain

Locality of Reference– If a data block has been recently

used, adjacent data will be needed soon

– Prefetch algorithm detects sequential data access patterns

Data Re-use– Accessed Data will probably be

used againLeast Recently Used– Flush old data from cache and

only keep active data in cache– Free up cache slots that are

inactive to make room for more active data

Cache is allocated in tracks referred to as cache slots, which are 32Kbytes in size (57 Kbytes for Mainframe). If the Symmetrix is supporting both FBA and CKD emulation within the same frame, the cache slots will equal the largest track size, 57K (3390). The Track Table is a directory of the data residing in cache and of the location/condition of the data residing on Symmetrix physical disk(s). Track Tables are used to keep the status of each track, and of each logical volume. Approximately 16 Bytes of cache space is used for each track.Prefetching is done by the Disk Director. Once sequential access is detected, prefetch is automatically turned on for that logical volume. Prefetch is initiated by 2 sequential accesses to a volume. Once turned on, for every sequential access, the Symmetrix will pull the next two successive tracks into cache (access to track 1 on cylinder 1 and will prompt the prefetch of tracks 2 & 3 on cylinder 1). After 100 sequential accesses to that volume, the next sequential access will initiate the prefetching of the next 5 tracks on that volume (access to track 1 on cylinder 10 will prompt the prefetch of tracks 2, 3, 4, 5 & 6 on cylinder 10). After the next 100 sequential accesses to that volume, the prefetch track value is increased to 8 (access to track 1 on cylinder 100 will prompt the prefetch of tracks 2, 3, 4, 5, 6, 7, 8 & 9 on cylinder 100). Any non-sequential accesses to that volume will turn the prefetch capability off.

As data is placed into cache or accessed within cache, it is given a pseudo timestamp. This allows the Symmetrix to maintain only the most frequently accessed data in cache memory. The data residing in cache is ordered through an Age-Link-Chain. As data is touched (read operation for example), it moves to the top of the Age-Link-Chain. Every time a director performs a cache operation, it must take control of the LRU algorithm. This forces the director to mark the least recently used data in cache to be overwritten by the next cache operation.




Read Operations

Read HitIn a read hit operation, the requested data resides in global memory. The channel director transfers the requested data through the channel interface to the host, and updates the global memory director. Since the data is in global memory, there are no mechanical delays due to seek, latency, and rotational position sensing that is encountered with disk.

Read MissIn a read miss operation, the requested data is not in global memory, and must be retrieved from a disk device. The disk director stores the data in global memory and updates the directory table. The Channel director then reconnects with the host and transfers the data. The host sends an acknowledgement and the directory tables are updated.




Write Operations

Fast Write On a write command, the channel director places the incoming blocks directly into global memory. The channel director sends an acknowledgement to the host. The directory tables are updated, and the disk director will asynchronously destage the data from global memory to the disk device.

Delayed fast WriteA delayed fast write occurs only when the fast write threshold has been exceeded. That is, the percentage of global memory containing modified data is higher than the fast write threshold. If this situation occurs, the Symmetrix system disconnects the channel director(s) from the channel. The disk directors then destage the Least Recently Used data to disk. When sufficient global memory space is available, the channel directors reconnect to their channels, and process the host I/O request as a fast write. The Symmetrix system continues to process read operations during delayed fast writes. With sufficient global memory present, this type of global memory operation rarely occurs.




Cache Allocation

Cache algorithms are designed to optimize cache utilization and “fairness” for all Symmetrix VolumesCache allocation dynamically adjust based on current usage– Symmetrix constantly monitors system utilization (including individual

volume activity)– “More active” volumes are dynamically allocated additional cache

resources from relatively “less active” volumes– Each volume has a minimum and maximum number of cache slots

for write operations

When a Symmetrix is IMPL’ed (Initial Microcode Program Load), the amount of available cache resources is automatically distributed to all of the logical volumes in the configuration. For example, if a Symmetrix were configured with 100 logical volumes of the same size and emulation, then at IMPL, each one would receive 1% of available cache resources. As soon as reads and writes to volumes begins, the Symmetrix Operating Environment (Enginuity) dynamically adjusts the allocation of cache. If only 1 of the 100 volumes was active, it would get incrementally more cache and the remaining amount would be redistributed to the other 99 volumes. Managing each individual volume’s write activity enables Enginuity to typically prevent system-wide delayed write situations.




Enginuity Overview

Operating Environment for Symmetrix– Each processor in each director is loaded with Enginuity

• Downloaded from service processor to directors over internal LAN• Zipped code loaded from EEPROM to SDRAM (control store of director)

– Enginuity is what allows the independent director processors to act as one Integrated Cached Disk Array• Also provides the framework for advanced functionality like SRDF,

TimeFinder,...etc.– All DMX ship with the latest Enginuity

5670.73.69

Symmetrix HardwareSupported:

50 = Symm352 = Symm455 = Symm556 = DMX

Microcode ‘Family’

(Major Release Level)

Field Release Level ofSymmetrix Microcode(Minor Release Level)

Field Release Level ofService Processor

Code(Minor Release Level)

Non-disruptive microcode upgrade and load capabilities are currently available for the Symmetrix. Symmetrix takes advantage of a multi-processing and redundant architecture to allow for hot loadability of similar microcode platforms. The new microcode loads into the EEPROM areas within the channel and disk directors, and remains idle until requested for hot load in control storage. The Symmetrix system does not require manual intervention on the customer’s part to perform this function. All channel and disk directors remain in an on-line state to the host processor, thus maintaining application access. Symmetrix will load executable code at selected “windows of opportunity” within each director hardware resource, until all directors have been loaded. Once the executable code is loaded, internal processing is synchronized and the new code becomes operational.




5670+ Management Features Enhancements

5670+ Management Features– End User Configuration

• User control of volumes and type– Symm Purge

• Secure deletion method– Logical Volumes

• Increased number of “hypers”– Volume Expansion

• Striped meta expansion

User Configuration - Enginuity v 5670+ will allow users to un-map CKD volumes, delete CKD volumes, or convert CKD volumes to FBA. These user configuration controls will simplify the task of reusing a Symmetrix by not requiring an EMC resource to modify the “bin” file.Symm Purge - provides customers a secure method of deleting (electronic shredding) sensitive data. This will simplify the reuse of drive assets.Logical Volumes - v 5670+ will support an increased number of hypers per spindle. The number of hypers will depend on the protection scheme. Volume Expansion - Previous microcode versions only supported the expansion of concatenated meta volumes. V5670+ will now support the expansion of both striped and concatenated meta volumes.




5670+ Business Continuity Features

5670+ Business Continuity Features– SRDF/A

• multi-session support – Protected Restore

• Enhanced restore features– SNAP Persistence

• Preserves snap session

SRDF/A- currently (v 5670) SRDF-A can only support a single-session. With v5670+ code, support will be available for multi-session SRDF/A data replication. Multi-session uses host control (Mainframe only). Cycle switching is synchronized between the single-session SRDF/A Symmetrix pairs.

Protected Restore- v 5670+ provides Protected Restore features. While the restore is in progress, read miss data will come from the BCV, writes to the Standard volume will not propagate to the BCV, and the original Standard to BCV relationship will be maintained.

SNAP Persistence - v 5670+allows a protected snap restore and preserves the virtual snap session when the restore terminates.




Configuration Considerations

Understand the applications on the host connected to the Symmetrix system– Capacity requirements– I/O rates– Read/Write ratios– Read/Write - Sequential or Random

Understand special host considerations– Maximum drive and file system sizes supported– Consider Logical Volume Manager (LVM) on the host and the use of data striping– Device sharing requirements - Clustering

Determine Volume size and appropriate level of protection– Symmetrix provides flexibility for different sizes and protection within a system– Standard sizes make it easier to manage

Determine connectivity requirements– Number of channels available from each host

Distribute workloads from the busiest to the least busy

The best possible performance will only be achieved if all the resources within the system are being equally utilized. This is much easier said than done, but through careful planning, you will have a better chance for success. Planning starts with understanding the host and application requirements. Within the Symmetrix bin-file, the emulation type, size in cylinders, count, number of mirrors, and special flags (like BCV, DRV, Dynamic Spare) are defined. Each Symmetrix Logical Volume is assigned a hexadecimal identifier. The bin file also tells the Channel director which volumes are presented on which port, and the address used to access it. From the Host’s perspective, when a device discovery process occurs, the information provided back to the OS appears to be referencing a series of SCSI disk drives. To an Open Systems host, the Symmetrix looks like a JBOD (Just a Bunch Of Disks). The host is unaware of the bin file, RAID protection, remote mirroring, BCV mirrors, dynamic sparing, ...etc. In other words, the host “thinks it’s getting” an entire physical drive.




Symmetrix Configuration Information

Symmetrix configuration information includes the following:

– Physical hardware that is installed –number and type of directors, memory, and physical drives

– Mapping of physical disks to logical volumes

– Mapping of addresses to volumes and to front-end directors

– Operational parameters for front-end directors

Configuration information is referred to as the IMPL.bin file or simply “the bin file”Stored in two places:

– On the Hard Disk of the Symmetrix Service Processor

– In the EEPROM of each Symmetrix Director

Configuration changes can also be made using EMC ControlCenter Configuration Manager GUI and Solutions Enabler CLI

Bin file stored in two places

Directors Service Processor

Two very important concepts:

Each director (both Channel and Disk) has a local copy (stored in EPROM) of the configuration file. This enables Channel Directors to be aware of the Disk Directors that are managing the physical copy(ies) of Symmetrix Logical Volumes and vice versa. The bin file also allows Channel Directors to map host requests to a channel address, or target and LUN to the Symmetrix Logical Volume.

Changes made to the bin file (non-SDR changes) must first be made to the IMPL.BIN on the Service Processor and then downloaded to the directors over the internal Ethernet LAN. Though Customer Service has the capability to do remote bin file updates (using the EMC Remote application), standard operating procedure mandates the CE be physically present for all configuration changes. In addition, CS requires that all CEs do a comparison analysis prior to committing changes (the existing IMPL.BIN is compared to the proposed IMPL.BIN).




Disk Performance Basics

Three components of disk performance– Time to reposition actuator - Seek time– Rotational latency– Transfer rate

With a Symmetrix, I/Os are serviced from cache not from the physical HDA– Minimizes the inherent latencies of

physical disk I/O– Disk I/O at memory speeds

+ Transfer Rate

Transfer Data

Position Actuator

Seek time Disk I/O =

time

+ Rotational Delay

Rotational Delay

When you look at a physical disk drive, a read or write operation has three components that add up to the overall response time.

Actuator positioning is the time it takes to move the read/write heads over the desired cylinder. This is mechanical movement and is typically measured in milliseconds. The actual time that it takes to reposition depends on how far the heads have to move, but this contributes to the greatest share of the overall response time.Rotational Delay is the time it takes for the desired information to come under the ready write head. This time is the function of the revolutions per second, or drive RPM. The faster the drive turns, the lower the rotational latency. A 10,000 RPM drive has an average rotational latency of approximately 3.00 milliseconds, which is half the time it takes to make one revolution.Transfer Rate is the smallest time component and consists of the time it takes to actually read/write the data. This is a function of drive RPM and the data density. It is often measured as internal transfer rate or external transfer rate. The external rate is the speed that the drive transfers data to the controller. This is limited by the internal transfer rate, but with buffers on the drive modules themselves, it allows faster transfer rates.

The design objective of a Symmetrix is to not limit the performance of host applications based on the performance limitations of the physical disk. This is accomplished using cache. Write operations are to cache and asynchronously destage to disk. Read operations are from cache using the Least Recently Used algorithm and prefetching to keep the information that is most likely to be accessed in memory.




Symmetrix Disk Comparisons

73 GB 146 GB181 GB73 GB36 GB18 GB36 GB 146 GB

FibreChannel

FibreChannel

FibreChannel

Ultra SCSIUltra SCSIUltra SCSIUltra SCSIUltra SCSIUltra SCSIInterface

DMXDMXDMXSym 5.XSym 5.XSym 5.XSym 5.XSym 5.XSym 4.8Symmetrix Architecture

10,00015,00010,00010,00010,00010,00010,00010,0007,200

Spindle Speed

73 GB

Symmetrix physical drives are manufactured by our supplier (Seagate, Hitachi) to meet EMC’s rigorous quality standards and unique product specifications. These specification include, dedicated microprocessors (that can be XOR capable), the most functionally robust microcode available, and large onboard buffer memory (4MB – 32MB).Again, while the physical speed of disk drives does contribute to the overall performance, the Symmetrix design is for most read or write operations to be handled from cache.




Mapping Physical Volumes to Logical Volumes

Symmetrix Physical Drives are split into Hyper Volume Extensions

Hyper Volume Extensions (disk slices) are then defined as Symmetrix Logical Volumes– Symmetrix Logical Volumes are internally labeled with hexadecimal identifier

(0000-FFFF)– Maximum number of Logical Volumes per Symmetrix configuration = 8192

Physical Drive

Logical Volume 4.2 GB

Logical Volume

4.2 GB



18 GB

While “hyper -volume” and “split” refer to the same thing (a portion of a Symmetrix physical drive), a “logical volume” is a slightly different concept. A logical volume is the disk entity presented to a host via a Symmetrix channel director port. As far as the host is concerned, the Symmetrix Logical Volume is a physical drive. Do not confuse Symmetrix Logical Volumes with host-based logical volumes. Symmetrix Logical Volumes are defined by the Symmetrix Configuration (BIN File). From the Symmetrix perspective, physical disk drives are being partitioned into Hyper Volumes. A Hyper Volume could be used as an unprotected Symmetrix Logical Volume, a mirror of a Symmetrix Logical Volume, a Business Continuance Volume (BCV), a parity volume for Parity RAID, a remote mirror using SRDF, a Disk Reallocation Volume (DRV), …etc. Host-based logical volumes are configured by customers through Logical Volume Manager software (Veritas LVM, NT Disk Administrator, ...etc.).

Note: In actuality, the true useable capacity of the drive would be less than 18GB due to disk formatting and overhead (track tables, etc.). This would result in each of the 4 splits in this example being approximately 4.21GB in size (open systems).




Symmetrix Logical Volume Specifications

Volume Specifications vary with Enginuity level– Enginuity allows up to 128 Hyper Volumes to be configured from

a single Physical Drive – Size of Volumes defined as number of Cylinders (FBA Cylinder =

15 * 32K), with a max. size ~32 GB– All Hyper Volumes on a physical disk do not have to be the same

size however a consistent size makes planning and ongoing management easier

Physical Disk

Physical Disk

Physical Disk

Physical Disk

Physical Disk

Volume specifications are illustrated here.




Defining Symmetrix Logical Volumes

Symmetrix Logical Volumes are configured using the service processor and SymmWin interface/application– EMC Configuration Group uses information gathered

during pre-site survey to create initial configuration• Generate configuration file (IMPL.BIN) that is downloaded from the service

processor to each director

Most configuration changes can be performed on-line at the discretion of the EMC Customer EngineerConfiguration changes can be performed online using the EMC ControlCenter Configuration Manager and Solutions Enabler Command Line Interface

Physical Disk

Physical Disk

Physical Disk

Physical Disk

Physical Disk

Symmetrix Service Processor

Running SymmWin Application

The C4 group (Configuration and Change Control Committee) is the division of Global Services responsible for initial Symmetrix configuration and any subsequent changes to the configuration. They use time-honored and extensive best practices and tools to configure Symmetrix. There is also much manual review to be done to ensure that BIN files are valid. An important misperception to correct is that only the CE can change the bin-file. While this might have been true at one time, today the customer may make configuration changes using EMC ControlCenter GUI or the Solutions Enabler CLI. Prior to 5x66 Enginuity, BIN file configuration was performed using a DOS-based program called AnatMain.




Symmetrix Logical Volume Types

Open Systems hosts use Fixed Block Architecture (FBA)– Each block is a fixed size of 512 bytes– Sector = 8 Blocks (4,096 Bytes)– Track = 8 Sectors (32,768 Bytes)– Cylinder = 15 Tracks (491,520 Bytes)– Volume size referred to by the number of Cylinders

Mainframes use Count Key Data (CKD)– Variable block size specified in “count”– Emulate Standard IBM volumes

• 3380D, E, K, K+, K++ (max. track size 47,476 bytes)• 3390-1, -2, -3, -9 (max. track size ~ 56,664 bytes)• Volume size defined as a number of Cylinders

Symmetrix stores data in cache in FBA and CKD and on physical disk in FBA format (32 KB tracks)– Emulates “expected” disk geometry to host OS through Channel

Directors

Data Block512 Bytes

DataCount Key

A notable exception to the “512-byte” Open Systems rule is AS/400. It uses 520 bytes per block. The extra 8 bytes are for host system overhead. Enginuity, prior to 5566 on the Symmetrix 5, only supports a single type of FBA format on Open Systems drives. If you connect an AS/400 to a pre-5566 Symmetrix, all FBA devices must be formatted 520. Open Systems hosts other than the AS/400 must be configured to use 520-formatted volumes. BE AWARE THAT CHANGING THE LOW-LEVEL FORMAT OF PHYSICAL DEVICES TYPICALLY REQUIRES SYMMETRIX DOWNTIME. Also, reformatting existing 512 devices will erase them, requiring a potentially complex backup and restore of all Open Systems data. With 5566+ on Symm 5 +, Enginuity has SLLF (Selective Low-Level Format) capabilities. This allows some drives to be formatted 512 and others 520, avoiding the complications mentioned above.The primary use for cache is for staging and destaging data between the host and the disk drives. Cache is allocated in tracks and is referred to as cache slots, which are 32Kbytes in size (57 Kbytes for Mainframe). If the Symmetrix is supporting both FBA and CKD emulation within the same frame, the cache slots will be the size of the largest track size, 57K (3390) track size.




Logical Volume 001

Logical Volume 002

Logical Volume 003

Logical Volume 00F

Meta VolumeLV 001

LV 002

LV 003

LV 00F

*Note: Symmetrix Engineering recommends Meta Volumes no larger than 512GB

Meta Volumes

Between 2 and 255* Symmetrix Logical Volumes can be grouped into a Meta Volume configuration and presented to Open System hosts as a single diskAllows volumes larger than the current maximum hyper volume size of 32GB– Satisfies requirements for

environments where there is a limited number of host addresses or volume labels available

Data is striped or concatenated within the Meta VolumeStripe size is configurable– 2 Cylinders is the default size,

which is appropriate for most environments

Meta Volumes allow customers to present larger Symmetrix Logical Volumes to the host environment. They are able to present more GBs with fewer channel addresses. There is a limitation on the number of volumes a host can manage. For example, with NT, the Drive lettering puts a limit on the number of volumes, and Meta Volumes prevent “running out of drive letters” by presenting larger volumes to NT hosts.




Data ProtectionData protection options are configured at the volume level and the same system can employ a variety of protection schemes

– Mirroring (RAID 1) • Highest performance, availability and functionality • Two mirrors of one Symmetrix Logical Volume located on separate physical drives

– Parity RAID• 3 +1 (3 data and 1 parity volume) or 7 +1 (7 data and 1 parity volume) • Formerly known as RAID S or RAID R

– RAID 5 –Striped RAID Volumes• Data blocks are striped horizontally across the members of the RAID (4 or 8 volume) group• No separate parity drive, parity blocks rotate among the group members

– RAID 10 – Mirrored Striped Mainframe Volumes– Dynamic Sparing

• One or more HDAs that are used when Symmetrix detects a potentially failing (or failed) device• Can be utilized to augment data protection scheme• Minimizes exposure after a drive failure and before drive replacement

– SRDF (Symmetrix Remote Data Facility)• Mirror of Symmetrix Logical Volume maintained in separate Symmetrix frame

RAID - Redundant Array of Independent DisksThe RAID Advisory Board has rated configurations with both SRDF and either Parity RAID or RAID 1 Mirroring with the highest availability and protection classification: Disaster Tolerant Disk System Plus (DTDS+)

See http://www.raid-advisory.com/emc.html for the ratings.




Mirroring: RAID-1

Two physical “copies” or mirrors of the dataHost is unaware of data protection being applied

Physical Drive

LV 001 M2

Different Disk Director

Physical Drive

LV 001 M1

Disk Director

Logical Volume 001

Host AddressTarget = 1LUN = 0

Mirroring provides the highest level of performance and availability for all applications. Mirroring maintains a duplicate copy of a logical volume on two physical drives. The Symmetrix maintains these copies internally by writing all modified data to both physical locations. The mirroring function is transparent to attached hosts, as the hosts view the mirrored pair of hypers as a single logical volume.

Prior to the Symmetrix DMX, mirrors were configured with what is known as the “rule of 17”. Because of where within the card cage the DA pairs reside (1/2, 3/4, 13/14, 15/16), as long as the sum of the DA director numbers equals 17 (1/16, 2/15, 3/14, 4/13), the mirrors will always be on different internal system buses for the highest availability and maximum Symmetrix resources. The Symmetrix DMX uses the rule of 17 for director failover pairing, and not volume mirroring. The point-to-point connections with cache eliminate the need for protection against a bus failure while mirroring volumes.




Mirror Positions

Internally each Symmetrix Logical Volume is represented by four mirror positions – M1, M2, M3, M4 Mirror position are actually data structures that point to a physical location of a mirror of the data and status of each trackEach mirror positions represents a mirror copy of the volume or is unused

Symmetrix Logical Volume 001

M1 M2 M3 M4M1 M3 M4

Before getting too far into volume configuration, understanding the concept of mirror positions is very important. Within the Symmetrix, each logical volume is represented by four mirror positions – M1, M2, M3, M4. These Mirror Positions are actually data structures that point to a physical location of a data mirror and the status of each track. In the case of SRDF, the mirror position actually points to a Logical Volume in the remote Symmetrix. Each position either represents a mirror or is unused. For example, an unprotected volume will only use the M1 position to point to the only data copy. A RAID-1 protected volume will use the M1 and M2 positions. If this volume was also protected with SRDF, three mirror positions would be used, and if we add a BCV to this SRDF protected RAID-1 volume, all four mirror positions would be used.




Physical Drive

Physical Drive

Logical Volume 000

Logical Volume 004

Logical Volume 008

Logical Volume 00C

LV 000 M1

LV 004 M1

LV 008 M1

LV 00C M1 LV 00C M2

LV 008 M2

LV 004M2

LV 000 M2

Mirrored Service Policy

Symmetrix leverages either or both mirrors of a Logical Volume to fulfill read requests as quickly and efficiently as possibleTwo options for mirror reads: Interleave and Split– Interleave maximizes throughput by using both Hyper Volumes for reads

alternately – Split minimizes head movement by targeting reads for specific volumes to

either M1 or M2 mirrorDynamic Mirror Service Policy (DMSP): policy is dynamically adjusted based on I/O patterns– Adjusted approximately every 5 minutes– Set at a logical volume level

During a read operation, if data is not available in cache memory, the Symmetrix reads the data from the volume chosen for best overall system performance. Performance algorithms within Enginuity track path-busy information, as well as the actuator location, and which sector is currently under the disk head in each device. Symmetrix performance algorithms for a read operation choose the best volume in the mirrored pair based on these service policies.

• Interleave Service Policy – Share the read operations of a mirror pair by reading tracks from both logical volumes in an alternating method: a number of tracks from the primary volume (M1) and a number of tracks from the secondary volume (M2). The Interleave Service Policy is designed to achieve maximum throughput.

• Split Service Policy – Different from the Interleave Service Policy because read operations are assigned to either the M1 or the M2 logical volumes, but not both. Split Service policy is designed to minimize head movement.

• Dynamic Mirror Service Policy (DMSP) -DMSP dynamically chooses between the Interleave and Split policies at the logical volume level based on current performance and environmental variables, for maximum throughput and minimum head movement. DMSP adjusts each logical volume dynamically based on recent access patterns. This is the default mode. The Symmetrix system tracks I/O performance of logical volumes (including BCVs), physical disks, and disk directors. Based on these measurements, it directs read operation for mirrored data to the appropriate mirror. As the access patterns and workloads change, the DMSP algorithm analyzes the new workload and adjusts the service policy to optimize performance.




Symmetrix RAID 10 (Mirrored Striped Mainframe Volumes with DMSP)

To improve mainframe volume performance, Symmetrix RAID 10 stripes data of logical devices across multiple Symmetrix logical devices. Four Symmetrix devices (each one-fourth the size of the original mainframe device) appear as one mainframe device to the host. Any four Symmetrix logical devices can be chosen to define a RAID 10 group provided they are the same type (for example, IBM 3390) and have the same mirror configuration. Striping occurs across this group of four devices with a striping unit of one cylinder, as shown in the diagram. Since each member of the stripe group is mirrored, the entire set is protected. Dynamic Mirror Service Policy (DMSP) can then be applied to the mirrored devices. The combination of DMSP with mirrored striping and concatenation to create a mainframe volume as illustrated, enables greatly improved performance in mainframe system




Symmetrix RAID-10 Meta volume

M1 M2Host I/O

Vol A Vol A

Vol A Vol A

Vol A Vol A

Vol A Vol A

Cylinders1, 5, 9…..








DMSP

This is a diagram of a RAID-10 stripe group. The portion of the logical volume which resides on one physical volume is called a stripe. Each RAID-10 stripe group consist of four stripes distributed across four physical volumes. These are mirrored to consist of eight total physical volumes. The stripe group is constructed by alternately placing one cylinder across each of the four physical volumes. These physical volumes cannot be on the same DA. The eight physical volumes are distributed across the Symmetrix back end for additional availability and improved performance. The DMSP feature, which is available in all Symmetrix systems, allows the Enginuity algorithms to dynamically optimize how the read requests can be satisfied over any of the eight physical devices.




Symmetrix Parity RAID

•3 +1 (3 data volumes and 1 parity volume) or 7 +1. •Parity calculated by Symmetrix Disk Drives using Exclusive-OR

(XOR) function.•Parity and difference data (result of XOR calculations) passed

between drives by DAs.•Member drives must be on different DA ports (ideally on

different DAs).•Parity volumes distributed across member drives in RAID

Group.

Vol A Vol B Vol C Parity

ABC

3 Host addressable volumes

+Not host addressable

Parity RAID is also referred to as RAID-S in Symmetrix 5 and earlier architectures. EMC’s Parity RAID DOES NOT STRIPE DATA. Parity RAID employs the same technique for generating parity information as many other commercially available RAID solutions, that is, the Boolean operation EXCLUSIVE OR (XOR). However, EMC’s Parity RAID implementation reduces the overhead associated with parity computation by moving the operation from controller microcode to the hardware on the XOR-capable disk drives.

Symmetrix Parity RAID is not offered as a performance solution• For high data availability environments where cost and performance must be balanced• Fixed 3 + 1 configuration means 25% of disk space used for protection• Avoid in application environments that are 25% or greater write intensive• Every write to a data volume requires an update (write) to the parity volume within that rank or group• Write activity to the parity volume equals the total writes to the 3 data volumes within that rank or group• In write intensive environments, the parity volume is likely to reach its Fast Write Ceiling sending the entire

rank into delayed write modeIf customer requirements dictate using Parity RAID, planning and careful attention to layout is required to ensure optimal performance. In some configurations, Parity RAID in a DMX environment may perform as well as RAID 1 protection on a Symmetrix 8000




Symmetrix RAID-5 (4 members)

Volume A

1 Host Addressable volume

Volume A with parity rotated among members

Parity 123 Data 1 Data 2 Data 3

Parity 456

Parity 789

Data 4 Data 5 Data 6

Data 7 Data 8 Data 9

Raid-5 Groups can have 4 or 8 members per logical device• 4 members per logical device = 3 RAID-5• 8 members per logical device = 7 RAID-5

This example shows a single Logical volume in a Raid-5 Group (Stripe width is 4 tracks).Note that the data and parity tracks of a RAID-5 device are striped across 4 members.No separate parity drive or volume; parity blocks rotate among the group members




Dynamic Sparing

Dedicated spare(s) disk protects storageDisk errors are detected during I/O operations or through DAs’ “Disk Scrubbing”Data from failed disk is copied to Dynamic SpareWhen failed disk is replaced, data is automatically restored and Dynamic Spare resumes role as standby

Dynamic Spare

Every Symmetrix logical volume has 4 mirror positions. There is no priority associated with any of these positions. They simply point to potential physical locations on the back end of the Symmetrix for the logical volume entity. When sparing is necessitated, hyper volumes on the spare disk devices take the next available mirror position for the logical volumes present on the failing volume. All of these dynamic spare hyper volumes are marked as having all tracks invalid in the respective mirror positions of the logical volumes. It is now the responsibility of the Symmetrix to copy all tracks over to the Dynamic Spare.

Dynamic sparing occurs at the physical drive level, since a physical drive is the FRU (Field Replaceable Unit) in the Symmetrix. In other words, you can’t just replace a failed hyper volume, only the disk it resides on. However, the actual data migration from the volumes on the failed drive to the dynamic spare occurs at the logical volume level.

Dynamic Sparing is also supported with Parity RAID, a minimum of 3 spares is suggested. If a drive fails, a dynamic spare drive will copy the data volumes onto itself by rebuilding them from parity and reading from any remaining uncorrupted data. If there are at least 3 spares available, the 1st spare will also start copying data from uncorrupted drives in the group. The other 2 spares will copy the contents of the remaining data volumes on the unaffected drives in the group. This results in the formerly parity-protected volumes now being temporarily mirrored. Since parity can’t be calculated with a drive lost, and mirroring is a faster way to make sure the data is redundantly protected, mirroring the entire RAID group results in the best way to protect against data loss until the problematic drive can be replaced.




SRDF IntroductionSymmetrix Remote Data Facility (SRDF) maintains real-time or near real-time copy of data at remote locationSimilar concept as RAID-1 except mirror is located in a different SymmetrixPrimary copy is called Source, remote copy is called TargetLink options between local and remote Symmetrix based on distance and performance requirements– ESCON– Fibre Channel– Gigabit Ethernet

Source Target

SRDF is an online, host-independent, mirrored data storage solution that duplicates production site data (source) to a secondary site (target). If the production site becomes inoperable, SRDF enables rapid manual fail over to the secondary site, allowing critical data to be available to the business operation in minutes. While it is easy to see this as a disaster recovery solution, the remote copy can also be used for business continuance during planned outages as well as backups, testing, and decision support applications. EMC offers a complete set of replication solutions to meet a wide range of service level requirements. When implementing a remote replication solution, users must balance application response time, recovery point objectives, and communications and infrastructure costs.




TimeFinder Introduction

TimeFinder allows local replication of Symmetrix Logical Volumes for business continuance operationsUtilizes special Symmetrix Logical volume called a BCV or Business Continuance Volume– BCV can be dynamically

attached to another volume, synchronized, and split off

– Host can access BCV as an independent volume that may be used for business continuance operations

– Full volume copy

1. “Establish” BCV 2. Synchronized3. “Split” BCV4. Execute BC operations

using BCV

STD BCV

BCV Split

BCV Established

STD BCV

TimeFinder uses Business Continuance Volumes (BCVs) to create copies of a volume for parallel processing. Basic TimeFinder operations include:

• Establish Mirror relationship between any standard volume and BCV. Basically, the BCV assumes the next available mirror position of the source volume. While a BCV is established, it is “hidden” from view and cannot be accessed.

• Synchronize data from Source to BCV. Synchronization will take place while production continues on the source volume. TimeFinder supports incremental establish by default where only changed data since the last establish is synchronized.

• Split allows the BCV to be accessed as an independent volume for parallel processing.• Restore allows the BCV to be established as a mirror to either the original source or a different volume and the

data on the BCV is synchronized.




EMC SNAP Introduction

EMC SNAP uses Snapshot techniques to create logical point-in-time images of a source volume– Snapshot is a virtual abstraction of a

volume– Multiple Snapshots can be created from

same source– Snapshots are available immediately

EMC SNAP does a Copy-on-Write– Writes to production volume are first

copied to Save Area– Uses only a fraction of the source

volume’s capacity (~20–30%)

Snapshots can be used for both read and write processing– Reads of unchanged data will be from

Production volume – Changed data will be read from Save Area

Save Area

Production view of volume

Snapshot viewof volume

Volume A

Original data copiedto Save Area prior to

new production writes

Snapshotof

Volume A(VDEV)

EMC Snap creates space-saving, logical point-in-time images or “snapshots.” The snapshots are not full copies of data; they are logical images of the original information based on the time the snapshot was created. It’s simply a view into the data. A set of pointers to the source volume data tracks is created instantly upon activation of the snapshot. This set of pointers is addressed as a logical volume and is made accessible to a secondary host that uses the point-in-time image of the data.




Symmetrix Availability: Phone-Home and Dial-In

EMC Phone-Home capability– Service Processor connects to

external modem – Communicates error and

diagnostic information to EMC Customer Service

– Provides problem resolutionDial-In capability– Product Support Engineer (PSE)

or Customer Engineer (CE) dial-in– Allows full control of service

processor through proprietary and secure interface

– Allows for proactive and reactive maintenance

– Can be disabled by customer through external modem

Every Symmetrix unit has an integrated service processor that continuously monitors the Symmetrix environment. The service processor communicates with the EMC Customer Support Center through a customer-supplied, direct phone line. The service processor automatically dials the Customer Support Center whenever Symmetrix detects a component failure or environmental violation. An EMC Product Support Engineer at the Customer Support Center can also run diagnostics remotely through the service processor to determine the source of a problem and potentially resolve it before the problem becomes critical. When required, a Customer Engineers will be dispatched to the Symmetrix to replace hardware or perform other maintenance.




Course Summary

The key points covered in this course include:Redundancy in the hardware design, and intelligence through Enginuity, allow Symmetrix to provide the highest levels of data availabilitySymmetrix basic architecture is comprised of three functional areas (Front End, Back End and Shared Global Memory) connected by internal system busesAll I/O must be serviced through cache (read hit, read miss, fast write, delayed write)Symmetrix physical disk drives are divided into Hyper Volumes, which form Symmetrix Logical Volumes, that are presented to the host environment as if they were entire physical drivesMirroring, Parity RAID, SRDF, and Dynamic Sparing are all media protection options available on Symmetrix

These are some of the main features of the Symmetrix. Please take a moment to read them.




Closing Slide

Thank you for your attention. This ends our training on Symmetrix Foundations.

Documents

Symmetrix Foundations Student Resource Guide