[linux-lvm] Problems creating/converting large logical volume to RAID1

[John Stoffel]

>>>>> "Zdenek" == Zdenek Kabelac <zkabelac at redhat.com> writes:

Zdenek> Dne 26.11.2015 v 11:29 Tony Arnold napsal(a):
>> John,
>> 
>> On 24/11/15 16:49, John Stoffel wrote:
>> 
>>> Can I make a suggestion to you?  Instead of trying to do the mirroring
>>> in LVM, build yourself an MD mirror, then layer LVM ontop of that
>>> instead.  You get nice seperation.
>>> 
>>> You can also take that /dev/sdb3, make it into an MD RAID1 array with
>>> just one device, add it into the VG, then move the LVs onto the new
>>> device.  Once that's done, you remove the sda3 from the VG, then add
>>> it into the MD device.  Something like this...
>>> 
>>>> mdadm --create /dev/md1 --level=1 --raid-devices=2 /dev/sdb3 missing
>>>> cat /proc/mdstat
>>>> pvcreate -v /dev/md1
>>>> vgextend -v vg0 /dev/md1
>>>> pvmove -v sda3
>>>> vgreduce -v vg0 sda3
>>>> mdadm --add /dev/md0 /dev/sda3
>>>> cat /proc/mdstat
>>> 
>>> And you will now be mirrored, etc.
>> 
>> Thanks for your suggestion which I have now implemented. The pvmove took
>> a few hours (1.5TB to move!) and then also some more hours while the
>> mirror set synchronised. But it's all done and I now have my volumes
>> mirrored.
>> 
>> I'm still curious though why the LVM based RAID1 didn't work. I'll just
>> have to stay curious!

Zdenek> 4.1  & 4.2  kernel has broken RAID

Zdenek> DO NOT USE  (at least with lvm2 - but since the flaw there is md driver
Zdenek> I assume mdadm is affected as well)

Zdenek> Switch to 4.3 please.

Was this fixed in 4.2.6 by any chance?  That's what I'm currently running...