On 08/08/2015 06:27 PM, Martin K. Petersen wrote:
"Heinz" == heinzm <heinzm@xxxxxxxxxx> writes:
Heinz,
+Discard Support
+---------------
+The implementation of discard support amoung hardware vendors varies. When
+a block is discarded, some storage devices will return zeros when it is
+read. These devices set the 'discard_zeros_data' attribute. Other devices
+will return random data. Confusingly, some devices will set
+'discard_zeros_data', but will still not always return zeros when
+discarded blocks are read!
This used to be correct but that's no longer the case. We only set
discard_zeroes_data when we have hard guarantees. We no longer
exclusively rely on what the device reports.
Martin,
so can we rely on discard_zeroes_data if reported 100% now?
Heinz
discard_zeroes_data is only set if the device reports LBPME/LBPRZ and
uses WRITE SAME 10 or 16 (SCSI) or if it reports DRAT/RZAT and is
explicitly whitelisted (ATA).
--
dm-devel mailing list
dm-devel@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/dm-devel
