06.12.2018 16:04, Austin S. Hemmelgarn пишет: > > * On SCSI devices, a discard operation translates to a SCSI UNMAP > command. As pointed out by Ronnie Sahlberg in his reply, this command > is purely advisory, may not result in any actual state change on the > target device, and is not guaranteed to wipe the data. To actually wipe > things, you have to explicitly write bogus data to the given regions > (using either regular writes, or a WRITESAME command with the desired > pattern), and _then_ call UNMAP on them.
WRITE SAME command has UNMAP bit and depending on device and kernel version kernel may actually issue either UNMAP or WRITE SAME with UNMAP bit set when doing discard.
