What is SSD TRIM?
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SSD TRIM is a SATA interface function that tells a SATA-interface flash SSD to begin a process of “garbage collection” using the program/erase cycle functions, usually as a background task. When a file is deleted from a computer, almost all operating systems simply delete the table of contents entry, but do not delete the actual data blocks from the storage media. For flash SSDs, this leaves unneeded data blocks on the flash media that will eventually need to be overwritten.
With TRIM, the operating system can direct a flash SSD to begin deleting unused blocks when the file is marked for deletion either immediately or as a background task. The goal is that unneeded blocks will be erased before they are needed, so that when writes occur later as files or data elements are saved, there will be plenty of empty blocks available for writing that don’t need to be erased first. Some, but not all operating systems support SSD TRIM natively today. In addition, many of the SSD vendors provide a utility application that can be run to accomplish this purpose. UNMAP is the equivalent term for SAS-interface SSDs.
This was first published in January 2012
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