On Tue, Sep 23, 2014 at 07:07:35PM -0400, Martin K. Petersen wrote: > >>>>> "Heinz" == heinzm <heinzm@xxxxxxxxxx> writes: > > Heinz> In case of RAID levels 4,5 and 6 we have to check for the > Heinz> capability to zero data on discards to avoid stripe data > Heinz> corruption. > > I'm quite concerned about relying on discard_zeroes_data since it's a > hint and not a hard guarantee. If we want to provide useful discards through raid we need to make it a hard guarantee. That is: - only set it when using a WRITE SAME variant on scsi - start adding a whitelist for ATA Relying on zeroout which also works when it doesn't unmap below is not the answer, especially if it may end up doing a physical write of zeroes on disk devices. Alternatively we could get rid of discard_zeroes_data and stop the pretence of any sane behavior from discard, and instead expose an unmap bit through the blkdev_issue_zeroout stack for those callers who want to do a discard, but rely on zeroes. The end effect will be the same, just a different presentation. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
