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PERGAMUM: REPLACING TAPE WITH ENERGY EFFICIENT, RELIABLE, DISK-BASED ARCHIVAL STORAGE. M. W. Storer K. M. Greenan E. L. Miller UCSC K. Vorugant Network Appliance. Summary. These slides only include what is missing in the Shockwave presentation: Background on MAID Glossary
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PERGAMUM: REPLACING TAPE WITH ENERGY EFFICIENT, RELIABLE,DISK-BASED ARCHIVAL STORAGE M. W. Storer K. M. Greenan E. L. MillerUCSC K. VorugantNetwork Appliance
Summary • These slides only include what is missing in the Shockwave presentation: • Background on MAID • Glossary • Two-level redundancy • Digital signatures • They are not self-sufficient
MAID • Massive Array of Idle Disks • Designed for Write Once, Read Occasionally applications. • Each disk is only spun up when a request is issued for the data on disk • Problems: • Less redundancy than RAID arrays • Frequent spin ups wear disks
Glossary (I) • Tome: • Basic hardware unit • Consists of • A low-power CPU with DRAM • A commodity SATA drive • A small flash drive • An Ethernet connection • Very autonomous
Glossary (II) • Blocks: • Much larger than conventional disk blocks • 128 KB to 1 MB • Will batch up small files into large files for archival storage • Normally done for tape drives (tar)
Glossary (III) • Segments: • Consist of a fixed number of blocks • Intra-disk parity is computed inside each segment • Includes one or two parity blocks
Glossary (II) • Regions: • Formed by a given number of segments • Basic building block for inter-disk redundancy
Intra-disk redundancy • Used to fix unrecoverable read errors (bad blocks) without spinning up disks of other tomes • Save energy • Reduce frequency of disk scrubbing operations • Can reconstitute contents of bad blocks
Inter-disk redundancy • Used to recover from disk failures • Recovery process is designed to minimize peak power consumption rather than total power consumption
Digital signatures • Include a timestamp (32 bits) • Stored in flash memory • Used to detect • Incorrect propagation of updates • Write errors