View
7.904
Download
3
Category
Preview:
DESCRIPTION
All about RAID
Citation preview
CPEG323 1
OVERVIEW
What is RAID?
Benefits of RAID
Concepts of RAID
RAID Levels
CPEG323 2
RAID AND ITS BENEFITS
What is RAID?
RAID (redundant array of independent disks; originally redundant array of inexpensive disks) is a way of storing the same data in different places (thus, redundantly) on multiple hard disks.
Benefits OF RAID Improved Performance High Availability Fault Tolerance
CPEG323 3
RAID CONCEPTS
STRIPING
MIRRORING
PARITY
CPEG323 4
RAID Concepts(Striping)
CPEG323 5
Raid Concepts (Mirroring)
All data in the system is written simultaneously to two hard disks instead of one; thus the "mirror" concept .
100% data redundancy which provides full protection against the
failure of either of the disks containing the duplicated data.
CPEG323 6
RAID Concepts(Parity)
Parity is redundancy information calculated from the actual data values.
take "N" pieces of data, and from them, compute an extra piece of data. Take the "N+1" pieces of data and store them on "N+1" drives. If you lose any one of the "N+1" pieces of data, you can recreate it from the "N" that remain, regardless of which piece is lost.
The parity calculation is typically performed using a logical operation called "exclusive OR" or "XOR".
CPEG323 7
RAID LEVELS
CPEG323 8
RAID: Level 0 (No Redundancy; Striping)
Multiple smaller disks as opposed to one big disk Spreading the blocks over multiple disks – striping – means that
multiple blocks can be accessed in parallel increasing the performance .
A 3 disk system gives 3 times the throughput of a 1 disk system
CPEG323 9
RAID: Level 0 (No Redundancy; Striping)
No redundancy, so what if one disk fails? Failure of one or more disks results in data loss.
RECOMMENDED APPLICATIONS
Video Production and Editing Image Editing Any application requiring high bandwidth
CPEG323 10
RAID: Level 1 (Redundancy via Mirroring)
Uses twice as many disks as RAID 0 (e.g., 8 smaller disks with second set of 4 duplicating the first set) so there are always two copies of the data
# redundant disks = # of data disks so twice the cost of one big disk
CPEG323 11
RAID: Level 1 (Redundancy via Mirroring)
What if one disk fails? If a disk fails, the system just goes to the “mirror” for the data
Recommended Application
Accounting
Payroll
Financial
Any application requiring very high availability
CPEG323 12
RAID: Level 2 (Redundancy via ECC)
ECC disks contain the parity of data on a set of distinct overlapping disks
# redundant disks = log (total # of data disks) so almost twice the cost of one big disk
- writes require computing parity to write to the ECC disks
- reads require reading ECC disk and confirming parity
Can tolerate limited disk failure, since the data can be reconstructed
blk1,b0 blk1,b2blk1,b1 blk1,b3Checks 4,5,6,7
Checks 2,3,6,7
Checks 1,3,5,7
3 5 6 7 4 2 1
10 0 0 11
ECC disks
0
ECC disks 4 and 2 point to either data disk 6 or 7, but ECC disk 1 says disk 7 is okay, so disk 6 must be in error
1
CPEG323 13
RAID: Level 3 (Bit-Interleaved Parity)
On RAID 3 systems, data blocks are subdivided (striped) and written in parallel on two or more drives. An additional drive stores parity information. You need at least 3 disks for a RAID 3 array.
writes require writing the new data to the data disk as well as computing the parity, meaning reading the other disks, so that the parity disk can be updated
Can tolerate limited disk failure, since the data can be reconstructed
reads require reading all the operational data disks as well as the parity disk to calculate the missing data that was stored on the failed disk
blk1,b0 blk1,b2blk1,b1 blk1,b3
10 01
(odd)bit parity disk
CPEG323 14
RAID: Level 3 (Bit-Interleaved Parity)
On RAID 3 systems, data blocks are subdivided (striped) and written in parallel on two or more drives. An additional drive stores parity information. You need at least 3 disks for a RAID 3 array.
writes require writing the new data to the data disk as well as computing the parity, meaning reading the other disks, so that the parity disk can be updated
Can tolerate limited disk failure, since the data can be reconstructed
reads require reading all the operational data disks as well as the parity disk to calculate the missing data that was stored on the failed disk
blk1,b0 blk1,b2blk1,b1 blk1,b3
10 0 1
(odd)bit parity diskdisk fails
1
CPEG323 15
RAID: Level 3 (Bit-Interleaved Parity)
Recommended Applications
Video Production and live streaming
Image Editing
Video Editing
Any application requiring high throughput
CPEG323 16
RAID: Level 4 (Block-Interleaved Parity)
RAID 4 improves performance by striping data across many disks in blocks, and provides fault tolerance through a dedicated parity disk.
CPEG323 17
RAID: Level 4 (Block-Interleaved Parity)
It is like RAID 3 except that it uses blocks instead of bytes for striping
Supports “small reads” and “small writes” (reads and writes that go to just one (or a few) data disk)
by watching which bits change when writing new information, need only to change the corresponding bits on the parity disk
the parity disk must be updated on every write, so it is a bottleneck for back-to-back writes
Can tolerate limited disk failure, since the data can be reconstructed
CPEG323 18
Small Writes RAID 3 small writes
New D1 data
D1 D2 D3 D4 P
D1 D2 D3 D4 P
3 reads and
2 writes involving all
the disks
RAID 4 small writesNew D1 data
D1 D2 D3 D4 P
D1 D2 D3 D4 P
2 reads and 2 writes
involving just two disks
CPEG323 19
RAID: Level 5 (Distributed Block-Interleaved Parity)
Parity is distributed across the disks Supports “small reads” and “small writes” (reads and writes that
go to just one (or a few) data disk) Allows multiple simultaneous writes as long as the
accompanying parity blocks are not located on the same disk
Can tolerate limited disk failure, since the data can be reconstructed
CPEG323 20
RAID: Level 5 (Distributed Block-Interleaved Parity)
Recommended Applications
File and Application servers
Database servers
Web, E-mail, and News servers
Intranet servers
Most versatile RAID level
CPEG323 21
Distributing Parity Blocks
By distributing parity blocks to all disks, some small writes can be performed in parallel
1 2 3 4 P0
5 6 7 8 P1
9 10 11 12 P2
13 14 15 16 P3
RAID 4 RAID 5
1 2 3 4 P0
5 6 7 P1 8
9 10 P2 11 12
13 P3 14 15 16
CPEG323 22
Raid : Level 6
RAID level 6 is an evolution of RAID 5. RAID 6 uses double parity for additional fault tolerance.
Like in RAID 5, data is striped at a block level across the disk sets while parity information is generated and written across the array. Now it's possible for more than one drive to fail simultaneously, and the RAID will still operate.
CPEG323 23
RAID: Level 6
Advantages Perfect solution for mission critical applications as it can sustain
multiple drive failures .
Disadvantages Uses 2 drives for parity
Recommended Applications Database server Mail server Web server Intranet server Transaction processing
CPEG323 24
RAID: Level 0+1 (Striping with Mirroring)
Combines the best of RAID 0 and RAID 1, data is striped across four disks and mirrored to four disks
Four times the throughput (due to striping) # redundant disks = # of data disks so twice the cost of one big
disk
writes have to be made to both sets of disks, so writes would be only 1/2 the performance of RAID 0
blk1 blk3blk2 blk4 blk1 blk2 blk3 blk4
redundant (check) data
CPEG323 25
RAID: Level 0+1 (Striping with Mirroring)
What if one disk fails? If a disk fails, the system just goes to the “mirror” for the data
Recommended Applications
Imaging applications
General fileserver
CPEG323 26
RAID: Level 1+0 (Mirroring with Striping)
RAID Level 10 provides very high performance and redundancy.
Data is simultaneously mirrored and striped. Can under circumstances support multiple drive failures.
CPEG323 27
THANK YOU
Queries?
Recommended