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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 the denser, but less reliable, multi-level cell technology.

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This was first published in December 2008

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