About reclaiming space on Solid State Devices (SSDs) with the TRIM operation

File systems that create and remove files often reuse storage blocks by overwriting a storage block with new contents. A Solid State Drive (SSD) device cannot overwrite a block of storage without erasing it first. This behavior causes a performance cost for writes to the previously used blocks, when compared to writes to unused or erased blocks. To avoid this cost, the TRIM operation informs the SSD which blocks of data are no longer in use and can be erased. The SSDs erase the unused blocks before the blocks are required for reuse, which improves the performance of the future write I/Os to the SSD. The TRIM operation also reduces wear leveling and fragmentation, because unused blocks are erased. The unused data does not get moved during a garbage collection or a cleaning cycle.

SF provides the TRIM operation only for supported devices. For more information, see the Symantec Hardware Compatibility List (HCL):

http://www.symantec.com/docs/TECH211575

The SF components, Veritas File System (VxFS) and Veritas Volume Manager (VxVM), use the TRIM operation to free up the blocks that do not contain valid data. The TRIM capability is similar to thin reclamation, and is performed with the same commands. The default SF reclamation commands perform TRIM for SSDs and thin reclamation for Thin Reclaimable LUNs. For file systems and volumes that use both SSDs and Thin Reclaimable LUNs, you can choose whether SF performs only a TRIM operation, only a thin reclamation, or both.

See Reclaiming space on a disk, disk group, or enclosure.

See Reclaiming space on a file system.

To display information about SSDs, use the vxdisk -o ssd list command. SF can also discover and display the disk space usage for Veritas File System (VxFS) file systems on SSDs. The VxFS file systems must be mounted on Veritas Volume Manager (VxVM) volumes. Use the vxdisk -o ssd -o fssize list command.

See the vxdisk(1M) manual page.