Looking for a life-save LVM Guru

[Chris Murphy]

On Fri, Feb 27, 2015 at 10:07 PM, Mike Wright
<nobody at nospam.hostisimo.com> wrote:
>
> I'd like to see it stay open.  The OP was not trolling and is obviously in
> desperate need of a solution.  I'm sure every one of us has lost critical
> data at one time or another.
>


I suggested closing this thread mainly because there were already a
bunch of replies on the centos list and seemed the best place to carry
on the discussion rather than fragmenting it.

I went ahead and tried to replicate the conditions (idealistically) in
a VM, with XFS, ext4, and Btrfs and simulated the failure.

tl;dr Btrfs faired the best by far permitting all data on surviving
drives to be copied off; the ext4 fs imploded at the first ls command
and nothing could be copied so it's a scrape operation, and XFS copied
~1/7 of the data, even though 3/4 of the drives were working.

The main solution, I think, in the LVM dead PV case is this command:
# vgchange -a y --activationmode partial

This makes the LV active with the PV missing. The least amount of
change in a case like this, the better, in order to avoid user induced
data loss (really, really common), so I don't recommend removing or
replacing the dead PV. If the LV type were mirror (legacy) or raid1,
then it would be a different story altogether.

Details are in the CentOS thread I previously included the URL for.

> LVM is still considered arcane by many and any shared wisdom regarding OP's
> situation would accrue greatly to our cumulative knowledge base.

Quite.

> I can attest that I once lost a volume that was so important to me that I
> got sick to my stomach.  I am loathe to wish that upon anyone.

Backups!

-- 
Chris Murphy