Trim (computing)

A trim command (known as TRIM in the ATA command set, and UNMAP in the SCSI command set) allows an operating system to inform a storage medium which blocks of data are no longer considered to be "in use" and therefore can be erased internally. TRIM is primarily used on solid-state drives (SSDs), but is also used on some shingled magnetic recording (SMR) hard drives. Trim commands were introduced soon after SSDs. Because SSDs use different technology from earlier magnetic hard drives, the preexisting techniques for storing data caused early SSDs to become slower as they were used more. With trimming, the SSD can efficiently clear unneeded data that would otherwise slow future write operations. Although tools to "reset" some drives to a fresh state were already available before the introduction of trimming, they also delete all data on the drive, which makes them impractical to use for ongoing optimization. As of 2010, many SSDs and many flash removable storage devices had internal garbage collection mechanisms for certain filesystem(s) (such as FAT and NTFS) that worked independently of trimming. Although this successfully maintained their lifetime even under operating systems that did not support trim, it had the associated drawbacks of increased write amplification and wear of the flash cells, as well as decreased write performance of flash cells.

A trim command (known as TRIM in the ATA command set, and UNMAP in the SCSI command set) allows an operating system to inform a storage medium which blocks of data are no longer considered to be "in use" and therefore can be erased internally. TRIM is primarily used on solid-state drives (SSDs), but is also used on some shingled magnetic recording (SMR) hard drives. Trim commands were introduced soon after SSDs. Because SSDs use different technology from earlier magnetic hard drives, the preexisting techniques for storing data caused early SSDs to become slower as they were used more. With trimming, the SSD can efficiently clear unneeded data that would otherwise slow future write operations. Although tools to "reset" some drives to a fresh state were already available before the introduction of trimming, they also delete all data on the drive, which makes them impractical to use for ongoing optimization. As of 2010, many SSDs and many flash removable storage devices had internal garbage collection mechanisms for certain filesystem(s) (such as FAT and NTFS) that worked independently of trimming. Although this successfully maintained their lifetime even under operating systems that did not support trim, it had the associated drawbacks of increased write amplification and wear of the flash cells, as well as decreased write performance of flash cells. An individual LBA range is called an LBA Range Entry and is represented by eight bytes. The LBA is expressed by the LBA Range Entry's first six bytes and the Range Length is a zero-based counter (e.g., 0=0 and 1=1) represented by the remaining two bytes. If the two-byte range length is zero, then the LBA Range Entry shall be discarded as padding. This means that for each 512-byte block of TRIM ranges that a device supports, the maximum is 64 ranges of 32 MB, or 2 GB. If a device supports SATA Word 105 at 8 then it should be able to trim 16 GB in a single TRIM (DATA SET MANAGEMENT) command. Fusion-io Patent "Apparatus, system, and method for redundant write caching" TRIM in SSD and SMR discs – about TRIM function in SSD and SMR drives

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