On Tue, Dec 22 2009 at 4:42pm -0500, Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > Martin, > > Apologies for the long mail here... > > On Tue, Dec 22 2009 at 12:41pm -0500, > Martin K. Petersen <martin.petersen@xxxxxxxxxx> wrote: > > > >>>>> "Mike" == Mike Snitzer <snitzer@xxxxxxxxxx> writes: > > > > Mike, > > > > Mike> OK, so is MD somehow getting things wrong? (You originally said > > Mike> that with the new stacking function MD resulted in an error but DM > > Mike> did not). > > > > MD is passing in absolute offsets and got the right result in both > > cases. > > > > > > Mike> "start" isn't a relative offset. > > > > It's relative to the beginning of the partition (block_device), not > > relative to the beginning of the disk (request_queue). > > Ah, thanks for clarifying! No idea why I thought "start" was relative > to the beginning of the disk (request_queue). > > > My beef here is that DM created a device like this: > > > > [root@10 ~]# pvs -o +pe_start > > PV VG Fmt Attr PSize PFree 1st PE > > /dev/sde1 foo lvm2 a- 508.00M 256.00M 192.00K > > /dev/sde2 foo lvm2 a- 512.00M 260.00M 192.00K > > [root@10 ~]# dmsetup table > > foo-bar: 0 1032192 striped 2 32 8:66 384 8:65 384 > > > > /dev/sde has an alignment_offset of 3584 > > /dev/sde1 has an alignment_offset of 0 > > /dev/sde2 has an alignment_offset of 1024 > > I'm seeing the following (when I use the scsi_debug from below): > # cat /sys/block/sdb/alignment_offset > 3584 > # cat /sys/block/sdb/sdb1/alignment_offset > 512 > # cat /sys/block/sdb/sdb2/alignment_offset > 512 Bleh, I used dev_size_mb=200 to get the above alignment_offsets. > > # modprobe scsi_debug dev_size_mb=1024 num_parts=2 lowest_aligned=7 physblk_exp=3 If I increase to dev_size_mb=500 I get: sdb1 alignment_offset=0 sdb2 alignment_offset=512 If I increase to dev_size_mb=1000 I also get: sdb1 alignment_offset=0 sdb2 alignment_offset=1024 Anyway, this doesn't change the fact that the new blk_stack_limits() isn't detecting the offset that DM provides as misaligned (in the legacy LVM case, data_alignment_offset_detection=0). In an earlier mail you said: dm_set_device_limits() calls blk_stack_limits() with a byte offset of 196608 for both sde1 and sde2. And that offset is checked for alignment with the queue's limits which has an alignment_offset of 3584. Applying that to this example that I shared: > The new blk_stack_limits() "works" (believes the device is aligned). > But if I use pvcreate w/ data_alignment_offset_detection=0 it > _incorrectly_ believes the device is aligned. > > Why does the new blk_stack_limits() think the misaligned offset is > aligned? I added some debugging to dm_set_device_limits() to see the > following: > > 1) MISALIGNED-case: LVM2 with data_alignment_offset_detection=0: > device-mapper: table: 254:1: target device sdb2 call to blk_stack_limits(): physical_block_size=4096, logical_block_size=512, alignment_offset=3584, start=104529920 > device-mapper: table: 254:1: target device sdb1 call to blk_stack_limits(): physical_block_size=4096, logical_block_size=512, alignment_offset=3584, start=212992 > > This is not properly aligned relative to physical_block_size=4096, sdb's > alignment_offset=3584 and each partitions' alignment_offset=512: > > >>> 104529920%4096 > 0 > >>> 212992%4096 > 0 dm_set_device_limits() calls blk_stack_limits() with a byte offset of 212992 for sdb1 and 104529920 for sdb2. And those offsets are checked for alignment with the queue's limits which has an alignment_offset of 3584. /me now goes to look at the new blk_stack_limits() -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
