On 27 May 2016 at 05:18, Darrick J. Wong <darrick.wong@xxxxxxxxxx> wrote: > > It's possible that the pvscsi device advertised WRITE SAME, but if the device > sends back ILLEGAL REQUEST then the SCSI disk driver will set > write_same_max_bytes=0. Subsequent BLKZEROOUT attempts will then issue writes > of zeroes to the drive. Thanks for following up on this but that's not what happens on the md device - you can go on to issue as many BLKZEROOUT requests as you like but the md disk is never zeroed nor is an error returned. I filed a bug at https://bugzilla.kernel.org/show_bug.cgi?id=118581 (see https://bugzilla.kernel.org/show_bug.cgi?id=118581#c6 for alternative reproduction steps that use scsi_debug and can be reworked to impact device mapper) and Shaohua Li noted that blkdev_issue_write_same could return 0 even when the disk didn't support write same (see https://bugzilla.kernel.org/show_bug.cgi?id=118581#c8 ). Shaohua went on to create a patch for this ("block: correctly fallback for zeroout" - https://patchwork.kernel.org/patch/9137311/ ) which has yet to be reviewed. -- Sitsofe | http://sucs.org/~sits/ -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
