Stefan Mileschin

The TRIM command feature has become an industry standard for internal garbage collection on SSDs. Unlike with magnetic storage devices such as hard drives, in NAND flash storage devices, new data can't simply be overwritten on existing deleted data (like overwriting on cassette tapes), instead NAND flash cells are first put through erase cycles, and then fresh data is written on them. This leads to degradation of performance in SSDs, as all deleted data will be put through erase cycles. The TRIM command allows the drive to tag freshly deleted data for disposal, and then erase flash memory occupied by that data when idling, and dynamically allocating erased cells for fresh data. This dramatically reduces write performance degradation of SSDs. Unfortunately, issuing TRIM commands to SSDs that are part of a RAID volume is so far not possible, because the RAID volume acts as a sort of an abstraction layer between the OS and physical disks. Some low-level data about member disks can still be read by diagnostic tools, but that's about it.

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