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 solid-state drive (SSD) which blocks of data are no longer considered in use and can be wiped internally. Areca RAID controller does not present physical drives to the operating system, only logical drives. The TRIM command requires direct access to the physical SSD device, and it is impossible when connected to an Areca RAID controller in RAID mode.
The UNMAP command needs to be supported by the OS, the drive, and the controller in order to work. The UNMAP command could result in higher SSD performance from both the reduced data needed to be rewritten during garbage collection and the higher free space resulting on the drive. The Areca RAID controller’s firmware has implemented the UNMAP between OS and controller so they can work UNMP commands if the OS supports them. This feature is now working with the ARC-1886 firmware. It can support UNMAP/WRITESAME for SAS/SATA/NVMe SSDs with any RAID/JBOD configurations.
Tags: firmware, SSD, TRIM, UNMAP, WRITESAME