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

[Cesare Leonardi]

Hello Ingo, I've made several tests but I was unable to trigger any 
filesystem corruption. Maybe the trouble you encountered are specific to 
encrypted device?

Yesterday and today I've used:
Debian unstable
kernel 4.19.20
lvm2 2.03.02
e2fsprogs 1.44.5

On 01/03/19 09:05, Ingo Franzki wrote:
> Hmm, maybe the size of the volume plays a role as Bernd has pointed out. ext4 may use -b 4K by default on larger devices.
> Once the FS uses 4K block anyway you wont see the problem.
> 
> Use  tune2fs -l <device> after you created the file system and check if it is using 4K blocks on your 512/512 device. If so, then you won't see the problem when moved to a 4K block size device.

I confirm that tune2fs reports 4096 block size for the 1 GB ext4 
filesystem I've used.
I've also verified what Bernd said: mkfs.ext4 still use 4096 block size 
for a +512M partition, but use 1024 for +500M.

As suggested by Stuart, I also made a test using a 4k loop device and 
pvmoving the LV into it. As you expected, no data corruption.
To do it I've recreated the same setup ad yesterday: 
/dev/mapper/vgtest-lvol0 on /dev/sdb4, a 512/512 disk, with some data on 
it. Then:
# fallocate -l 10G testdisk.img
# losetup -f -L -P -b 4096 testdisk.img
# pvcreate /dev/loop0
# vgextend vgtest /dev/loop0
# pvmove /dev/sdb4 /dev/loop0
# fsck.ext4 -f /dev/mapper/vgtest-lvol0

While I was there, out of curiosity, I've created an ext4 filesystem on 
a <500MB LV (block size = 1024) and I've tried pvmoving data from the 
512/512 disk to 512/4096, then to the 4096/4096 loop device.
New partitions and a new VG was used for that.

The setup:
/dev/sdb5: 512/512
/dev/sdc2: 512/4096
/dev/loop0 4096/4096

# 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

# blockdev -v --getss --getpbsz --getbsz /dev/loop0
get logical block (sector) size: 4096
get physical block (sector) size: 4096
get blocksize: 4096

# pvcreate /dev/sdb5
# vgcreate vgtest2 /dev/sdb5
# lvcreate -L 400M vgtest2 /dev/sdb5
# mkfs.ext4 /dev/mapper/vgtest2-lvol0

# tune2fs -l /dev/mapper/vgtest2-lvol0
[...]
Block size:               1024
[...]

# mount /dev/mapper/vgtest2-lvol0 /media/test
# cp -a SOMEDATA /media/test/
# umount /media/test
# fsck.ext4 -f /dev/mapper/vgtest2-lvol0

Now I've moved data from the 512/512 to the 512/4096 disk:
# pvcreate /dev/sdc2
# vgextend vgtest2 /dev/sdc2
# pvmove /dev/sdb5 /dev/sdc2
# fsck.ext4 -f /dev/mapper/vgtest2-lvol0

No error reported.
Now I've moved data to the 4096/4096 loop device:
# pvcreate /dev/loop0
# vgextend vgtest2 /dev/loop0
# pvmove /dev/sdc2 /dev/loop0
# fsck.ext4 -f /dev/mapper/vgtest2-lvol0

Still no data corruption.

Cesare.