The trouble with discard

One point which wasn't brought up in the article is that while several filesystems have implemented calls to discard, the only devices which currently implement discard (in mainline) are MTD. There are significant problems with implementing TRIM for ATA devices, most notably that because it sits below the SCSI layer, ideally one would implement the SCSI UNMAP command, and then translate that into the ATA TRIM command. Because the 'data' sent to the device is completely different, one would need to change the length of the data -- something the Linux SATL seems completely incapable of doing.