Storage - Effective Storage for Efficient Databases Hakan...

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Effective Storage for Efficient Databases Hakan Ferhatosmanoglu CSE 671
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RAID Technology Parallelizing disk access Data Striping Distribute data over several disks to give the impression of having a single large, very fast disk. Multiple I/Os to be services in parallel High transfer rates Load balancing among disks
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RAID Technology Probability of failure is high Array of n disks Prob(failure) is n times as much as that for 1 disk Mean time to failure For a single disk: 200,000 hours (22 years) 100 disks ?? Reliability through redundancy Store redundant info on disks – Replication, parity or some other error correcting codes
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Improving reliability with RAID Store redundant info (not just a single copy of data) Disadvantages: Additional I/O for writes Extra cost for maintaining redundancy and recovery from errors More storage
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Improving reliability with RAID Techniques: Mirroring or Shadowing (Replication) Store data to 2 identical disks (treated as one logical disk) Read data from the disk with shorter queuing, seek, etc. If one fails, use the other. Store extra info to reconstruct lost info in case of disk failure (Error correcting codes)
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RAID Technology Disk Striping is usually at block level but bit-level striping is also possible 8 bits, 8 disks jth bit to the jth disk 8 times speedup RAID level 0 to level 6
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RAID Technology Level 0: No redundancy Data striping Best write performance (only single update) Good (sometimes not so good) read performance! Why?
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Storage - Effective Storage for Efficient Databases Hakan...

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