[linux-lvm] Need help with a particular use-case for pvmove.

Stirling Westrup swestrup at gmail.com
Sun Nov 14 03:56:05 UTC 2010

On Sat, Nov 13, 2010 at 6:03 PM, Lars Ellenberg
<lars.ellenberg at linbit.com> wrote:
> On Sat, Nov 13, 2010 at 04:45:36PM -0500, Stirling Westrup wrote:

>> All I want to do is move physical extents from one physical volume to
>> another. Both of those volumes are present and accessible. Why should
>> uninvolved missing volumes be an issue, and is there any way around
>> it?  pmmove suggests running "vgreduce --removemissing" but the
>> documentation for vgreduce seems to say that I'd need to 1) use
>> --force and 2) it would likely result in data loss.
>> Is there anything I can do, short of borrowing another storage array
>> somewhere, just so I can have an extra slot to do this move? My other
>> option is to put the new drive into a USB case, but the server only
>> supports USB1, so moving a terrabyte will take over a week.

> If you do it offline anyways:
> Shut down.
> Unplug one of the good old drives, plug in the new drive.
> If you want to be extra sure against typos,
> unplug all but the bad-old drive ;-)
> Boot into maintenance mode, use a live-cd if you have to.
> Don't activate the VG.  It won't activate with one pv missing anyways,
> unless you really want it to.
> Then dd_rescue copy the disk image from bad-old to new, including
> everything (partition table, if any, LVM signature, the full image).
> Remove bad-old drive, have all other old and the new plugged,
> reboot normally.
> Done.
> Estimated downtime, assuming a sustained linear write speed of 80 MiB/s:
> 1 TiB / (80 MiB/s), well under 4 hours.

Thanks. I did consider this, but the new drive is twice the size of
the old one, so I would need to make sure I had created a partition on
the new drive the exact size of the old one, and had dd-ed everything
correctly. Even then, I wasn't sure if it would work, because I don't
know what the metadata records in terms of the drive configurations.

Stirling Westrup
Programmer, Entrepreneur.

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