UC Santa Cruz

Reliability of MEMS-Based Storage Enclosures

Bo Hong, Thomas J. E. Schwarz, S. J.*

Scott A. Brandt, Darrell D. E. Long

Storage Systems Research Center

University of California, Santa Cruz

*Also Santa Clara University, Santa Clara, CA

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MEMS Storage Technology Micro-Electro-Mechanical Systems (MEMS) storage

• A promising alternative secondary storage technology• Hardware Research: IBM, HP, CMU, Nanochip• Magnetic storage, but very different mechanics

Spring

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MEMS Storage Technology MEMS-based storage vs. Magnetic Disk

• Provides non-volatile storage, too.• Delivers 10 * faster access time (< 1 ms)• Delivers higher bandwidth (100 MB – 1 GB/s)• Small (size of penny, cent)• Consumes 100* less power• Costs ~10 USD per device• Expected to be more reliable

• Stores limited amount of data per device (3-10 GB)

A serious alternative to disk drives, in particular for mobile computing applications

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Reliability Implication of MEMS-based Storage Storage systems built from MEMS-based storage …

• Require more MEMS devices At least 10 times the number of disks to meet capacity requirements

• Require more connection components Reliability implication

• More components, hence (?) lower reliability

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MEMS Storage Enclosure

Our proposal: MEMS Enclosures• A device with dozens of MEMS• Single interface to rest of system• Might be serviceable, but service calls

during economic lifetime should be very rare

Interface

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MEMS Storage Enclosures Reliability an issue:

• MTTF 1- 2 years without redundant data storage Uses RAID Level 5 technology with distributed sparing

• Additional k spares Calls for service when necessary

• i.e. when we run out of spares Organization and number of spares can

• Decrease the data recovery time and thus improve reliability• Reduce human interference

No errors servicing Reduce maintenance costs

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MEMS Enclosure Reliability

Measure MTBF for enclosures • Without replacing spares• With replacing spares (service calls)

Determine number of failures that trigger a service call

Mandatory replacement: no redundancy left Preventive replacement: no spare left

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MEMS Enclosure Reliability without Replacement

Disk23 Yrs

3 spares5.8 Yrs

2 spares4.6 Yrs

No spare2.3 Yrs

1 spare3.5 Yrs

4 spares6.9 Yrs

Disk11.5 Yrs

5 spares8.1 Yrs

MTTFDISK = 11.5 or 23 yrs

MTTFMEMS = 23 yrs 19 data + 1 parity + k

dedicated spares 15-minute data

recovery

MTTF is not enough to measure reliability of enclosures without repairs

Instead: focus on data reliability during the economic lifetimes (3-5 years) of enclosures

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MEMS Enclosures with Replacement Markov model for a MEMS enclosure with N data,

one parity, and one dedicated spare devices• N – Normal; D – Degraded; DL – Data Loss• 1/ – MTTFMEMS (in tens of years)• 1/µ – Mean Time Between Recovery (in minutes)• 1/ – Mean Time Between Replacement (in days, weeks)

Preventive and mandatory replacement

Preventive replacement

Mandatory replacement

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MEMS Enclosure Reliability with Replacement

Preventive replacement increases reliability and reduces replacement urgency

No spare

Preventive + mandatory

Mandatory21

3

3

1 2

1, 2, 3 – Number of spares

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MEMS Enclosure Reliability

Dedicated Sparing• Replace all data from a failed MEMS

on a single spare MEMS Distributed Sparing

• Every spare contains Client data Parity data Spare space

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Distributed Sparing [Menon and Mattson 1992]

Before failure

X

Shorter data recovery time More devices can fail

After MEMS 4 fails

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Reliability Comparison: Dedicated Sparing vs. Distributed Sparing

No spare

Preventive + mandatory

MandatoryDedicated

Dedicated

1

2

2

1

1, 2– Number of spares

Compare with following slide

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Reliability Comparison: Dedicated Sparing vs. Distributed Sparing

Distributed sparing only better at short replacement times when using preventive replacement

No spare

Dedicated &Distributed

Dedicated

Distributed

1

2

2

1

1, 2– Number of spares

Preventive + mandatory

Mandatory

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All about economy• How long can MEMS enclosures work without repairs?• How often do they need repairing in the first 3-5 years?• How does replacement policies affect maintenance

frequency?

# of failures an enclosure with k spares can tolerate before the (m+1)th repair is scheduled (m >= 0):• (m + 1) × k, under the preventive replacement policy• (m + 1) × (k + 1), under the mandatory replacement

policy

Durability of MEMS Storage Enclosures

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Durability of MEMS Storage Enclosures

Probabilities that a MEMS storage enclosure has up to k failure during (0, t]

2 failures

4 failures

6 failures

1 failure

Disk23 Yrs

No failure

8 failures

10 failures

First year survivability: 95.7% of disk vs. 98.8% of MEMS enclosures with two spares

Chance that MEMS enclosure with four spares requires more than one service in five years: 3.5% (preventive) vs. 0.6% (mandatory)

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Related Work MEMS-based storage technology development

• IBM, HP, CMU CHI2PS, Nanochip Digital Micromirror Devices by TI

• Reported Mean Time Between Failure: 650,000 hours [Douglass]

RAID reliability• Dedicated sparing [Dunphy et al.]• Distributed sparing [Menon and Mattson]• Parity sparing [Reddy and Banerjee]

Disk failure prediction• S.M.A.R.T (Self-Monitoring Analysis and Reporting

Technology)

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Summary Reliability of MEMS storage enclosures

• Can be more reliable than disks even without failed device replacement

• Highly reliable when using preventive replacement • Dedicated sparing and distributed sparing provide

comparable or almost identical reliability Economy of MEMS storage enclosures

• Preventive replacement trades more maintenance services for higher reliability

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Thank You! Acknowledgements

• Dave Nagle, Greg Ganger, CMU PDL• The rest of the UCSC SSRC

More information:• http://ssrc.cse.ucsc.edu• http://ssrc.cse.ucsc.edu/mems.shtml

Questions?

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Backup Slides

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MEMS Storage Technology Micro-Electro-Mechanical Systems (MEMS) storage

• A promising alternative secondary storage technology• Hardware Research: IBM, HP, CMU, Nanochip

Radical differences between MEMS storage and magnetic disk technologies

Disk MEMSRecoding

mediaMagnetic

Magnetic or physical(non-volatile)

Recoding technique

LongitudinalOrthogonal

(higher density)

R/W head SingleThousands – tip array

(Higher bandwidth and parallelism)

Media movement

RotationMedia sled moves in X and Y independently

(no rotation delay)

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MEMS Storage Device Characteristics Physical size: 1 – 2 cm2

Recording density: 250 – 750 Gb/in2

7GB/s

1ns 10ns 100ns 1us 10us 100us 1ms 10ms

1GB/s

2GB/s

3GB/s

4GB/s

5GB/s

6GB/s

Th

rou

ghp

ut

DRAM

DISK

MEMS

Predicted Performance in 2005

Access Latency

0.5–2 GB$100-$200/

GB

3–10 GB$5-$50/

GB100–500

GB$1-$2/GB

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MEMS Storage Device

Spring

X

Y

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Durability of MEMS Storage Enclosures

Probabilities that a MEMS storage enclosure has up to k failure during (0, t]

2 failures

4 failures

6 failures

1 failure

Disk23 Yrs

No failure

8 failures

10 failures