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Vol. 7 No. 10 December 2008

Storage 101

Why solid-state drives wear out Unlike hard disk drives, flash solid-state drives (SSDs) don't contain spinning parts. Instead, data is written to cells in an SSD, which is made up of flash memory chips. These cells have a finite lifecycle, and each one can be written to only so many times before it wears out, eventually becoming unprogrammable. (DRAM-based solid state doesn't have the same wear-out issues as flash.) Vendors work around this wear-out hurdle in different ways, often using controllers. Techniques include wear-leveling algorithms to distribute workload across all cells, or extra substitute cells that can be used for wear leveling and cell healing, which, when paired with error correction codes, can detect and correct any damaged cells as they're read. In addition, SSDs might be set up similar to RAID, with striping across several drives to mitigate any loss due to wear-out failure. Flash SSDs are currently usually single-level cell, which have one bit per cell and can get up to 10 times as many lifetime writes as ...

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Features in this issue

  • LTO-4 gains favor among tape drive buyers

  • How your SAN will evolve

    We asked storage vendors, industry analysts and technologists serving on storage industry associations about where they saw the SAN heading. There may not be sweeping architectural changes in five years, but there will be changes in the basic building blocks of the SAN infrastructure: networks and protocols; switches; storage arrays, disks and controllers; and SAN management.

  • "I second that VMotion," say replication vendors

    Replication vendors are finding new avenues for their technology by leveraging VMware's VMotion technology.

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