[linux-lvm] lvconvert -m 0 /dev/varlin/distfiles /dev/md0 => zero filled logical volume

[Raimonds Cicans]

On 16.03.2016 23:36, Raimonds Cicans wrote:
> I am trying to move LVM setup from old RAID md0 to new RAID md1
>
> I did "lvconvert -m 1 /dev/path/to/logical_volume /dev/md1" on bunch of
> logical volumes.
> Everything went without problems.
>
> Then I tried to remove md0 from one of logical volumes by running command:
> lvconvert -m 0 /dev/varlin/distfiles /dev/md0
>
> I tried to mount this logical volume, but failed.
>
> Then I checked first  megabyte of logical volume it was zero filled.
>
> Partial output of "lvs -o+devices":
>    LV              VG     Attr       LSize   Pool Origin Data%  Meta%
> Move Log Cpy%Sync Convert Devices
>    backup          varlin -wi-ao---- 100,00g
> /dev/md0(6304)
>    backup          varlin -wi-ao---- 100,00g
> /dev/md0(8544)
>    data            varlin -wi-ao----  20,00g
> /dev/md0(28384)
>    distfiles       varlin -wi-a-----  20,00g
> /dev/md1(2738)
>    ftp             varlin rwi-aor---  10,00g         100,00
> ftp_rimage_0(0),ftp_rimage_1(0)
>    ftpdown         varlin rwi-aor---  10,00g         100,00
> ftpdown_rimage_0(0),ftpdown_rimage_1(0)
>
>
> lvm2: 2.02.116
> kernel: 4.4.2
>
>

I made following test:
I unmounted /opt and dumped to files following volumes:
/dev/mapper/varlin-opt
/dev/mapper/varlin-opt_rimage_0
/dev/mapper/varlin-opt_rimage_1

and then diff-ed them.

/dev/mapper/varlin-opt_rimage_0 was not equal with /dev/mapper/varlin-opt.
Why??? I thought 100 in Cpy%Sync column of lvs output mean volume is 
fully synchronized.

With "lvconvert -m0" I removed /dev/mapper/varlin-opt_rimage_0 from 
/dev/mapper/varlin-opt.

I did some test of volume - everything was normal.

My plan for now:
for each mirrored volume:
1) do volume content backup
2) umount volume
3) run md5sum for volume itself and all mirror sub-volumes
4) with "lvconvert -m0" remove sub-volume which is not equal to volume
5) do some volume tests
6) if something went wrong - restore volume content from backup
7) if on step 4 was removed new RAID md1, then make pvmove to md1


Best regards,
Raimonds Cicans