6/5/2008 1 trap-array: a disk array architecture providing timely recovery to any point-in-time...
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6/5/2008 1
TRAP-Array: A Disk Array Architecture Providing Timely Recovery to Any Point-in-time
Authors: Qing Yang,Weijun Xiao,Jin Ren University of Rhode Island
Presented By: Anuradharthi T
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Outline Introduction Background Related Work TRAP- 4 Architecture Results Conclusion
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IntroductionRAID Architecture
- Most prominent architecture advance in disk I/O
systems
- In use for more than two decades
- Types of RAID: RAID1- provides 2N data redundancy to protect data RAID3, 4 & 5- store data in parity stripes across
multiple disks to improve space
efficiency & performance
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RAID Architecture Advantages:
- Can recover data from more than one disk failure- Improves data reliability
Disadvantages:- Recovery not possible when damaged data are not confined to 1 or 2 disks- Accounts for 60% to 80% of data losses- Examples of such damages are: software defects,
virus attacks, power failure or site failure
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Solution
Timely Recovery to Any Point-in-time(TRAP)- Keep log of all previous versions of changed data
blocks in time sequence- Utilizes a fast & simple encoding scheme
=> less space- Provides faster data recovery to any-point-in-time due to
drastically smaller amount of storage space used =>improved performance
- Thus achieves an optimal space & performance characteristics
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BackgroundRecovery of data in real world is measured by ‘2’
key parameters:1. RPO (Recovery Point Objective)
- measures maximum acceptable age of data at time of outage
2. RTO (Recovery Time Objective)
- maximum acceptable length of time to resume normal data processing operations after an outage
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Classification of storage architecture Storage architectures are capable of recovering
data upon an outage Based on the 2 key parameters
TRAP-1 TRAP-2 TRAP-3 TRAP-4
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Related work TRAP-1
Uses periodical backups & snapshots Time consuming & degrades application performance Data transferred to tapes or disk for backup
TRAP-2 Performs file versioning that records a history of changes to files Versioning has to be done manually Have controllable RTO & RPO File system dependent
TRAP-3 Keep a log of changed data for each data block in a time sequence
(time stamps) Continuous Data Protection (CDP) Huge amount of storage space required
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TRAP-4 Architecture
Keeps a log of parities as a result of each write on the block Suppose a host writes into data block with logic address Ai
that belongs to a data stripe (A1,A2….Ab….An) RAID controller perform the parity calculation as follows:
Where, PT(k) – new parity for corresponding stripe
Ai(k) – new data for data block Ai
Ai(k-1) – old data of data block Ai
PT(k-1) – old parity of the stripe
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Optimizing the parity P’T(k)= is appended to the parity log stored in the TRAP disk after a simple encoding Only 5% to 20% of bits inside a data block actually change on a write operation Parity P’T(k) reflects the exact changes at bit level of new write operation on the existing block As a result, this parity block contains mostly zeros with a very small portion of bit stream that is nonzero Thus it can be easily encoded to a small size parity block to be appended to the parity log reducing the amount of storage space
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Block Diagram of TRAP-4 design
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Recovery on outage Consider the parity log corresponding to a data block, Ai
after a series of write operations. Log contains P’T(k) P’T(k-1) …. P’T(2) P’T(1) with timestamps
T(k), T(k-1), …. T(2) and T(1) associated with parities When an outage occurs at time t1, and we would like to
recover data as at time t0 (t0 < t1)
Note that for all l = 1,2, … r
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System Architecture of TRAP-4
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Experimental Setup
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File System micro benchmarks
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Data size comparison
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Data Reduction ratio
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Retrieval time comparison
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Conclusions A new disk array architecture capable of providing
timely recovery to any point-in-time for user data stored in array
Up to 2 orders of magnitude improvements in terms of storage efficiency
Has quick recovery time Provides continuous data protection capability
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Thank You