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From: Zdenek Kabelac <zkabelac@redhat.com>
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Date: Thu, 26 Nov 2015 15:07:52 +0100
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Subject: Re: [linux-lvm] Problems creating/converting large logical volume
	to RAID1
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To: LVM general discussion and development <linux-lvm@redhat.com>

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!

4.1  & 4.2  kernel has broken RAID

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

Switch to 4.3 please.

Regards

Zdenek