[linux-lvm] Filesystem corruption with LVM's pvmove onto a PV with a larger physical block size

[Cesare Leonardi]

On 28/02/19 09:41, Ingo Franzki wrote:
> Well, there are the following 2 commands:
> 
> Get physical block size:
>   blockdev --getpbsz <device>
> Get logical block size:
>   blockdev --getbsz <device>

I didn't know the blockdev command and, to recap, we have:
--getpbsz: physical sector size
--getss: logical sector size
--getbsz: blocksize used internally by the kernel

getpbsz/getss correspond to physical/logical sector size reported by 
fdisk, smartctl, etc.

> Filesystems seem to care about the physical block size only, not the logical block size.
> 
> So as soon as you have PVs with different physical block sizes (as reported by blockdev --getpbsz) I would be very careful...

I've done the test suggested by Stuart and it seems to contradict this.
I have pvmoved data from a 512/512 (logical/physical) disk to a newly 
added 512/4096 disk but I had no data corruption. Unfortunately I 
haven't any native 4k disk to repeat the same test.

Here is what I've done.
/dev/sdb: SSD with 512/512 sector size
/dev/sdc: mechanical disk with 512/4096 sector size

# blockdev -v --getss --getpbsz --getbsz /dev/sdb
get logical block (sector) size: 512
get physical block (sector) size: 512
get blocksize: 4096

# blockdev -v --getss --getpbsz --getbsz /dev/sdc
get logical block (sector) size: 512
get physical block (sector) size: 4096
get blocksize: 4096

# pvcreate /dev/sdb4
# vgcreate vgtest /dev/sdb4
# lvcreate -L 1G vgtest /dev/sdb4
# mkfs.ext4 /dev/mapper/vgtest-lvol0
# mkdir /media/test
# mount /dev/mapper/vgtest-lvol0 /media/test
# cp -a SOMEDATA /media/test/
# umount /media/test
# fsck.ext4 -f /dev/mapper/vgtest-lvol0

Filesystem created and no error on it. Now the disk with different 
physical size:

# pvcreate /dev/sdc1
# vgextend vgtest /dev/sdc1
# pvmove /dev/sdb4 /dev/sdc1
# fsck.ext4 -f /dev/mapper/vgtest-lvol0
# mount /dev/mapper/vgtest-lvol0 /media/test
# ls /media/test/

The fsck command reports no errors, the filesystem is mountable and the 
data is there.

Looks like physical sector size didn't matter here. Or I'm missing 
something?

Cesare.