[linux-lvm] Fun and games with mirroring

[Les Mikesell]

On Wed, May 23, 2012 at 3:54 AM, Bryn M. Reeves <bmr at redhat.com> wrote:
>
>> I'm not looking to have a LVM snapshot. I'm looking to have a
>> duplicate disk. This allows me to experiment on one, whilst keeping
>> the other safe.
>
> That's exactly what snapshots do.

If your experiment involves reinstalling an OS that reformats one of
the drives, what will that do to your snapshot?

With MD raid1 you can just pull one of the mirrors and you are pretty
safe.   Although I'm beginning to like ReaR
(http://rear.sourceforge.net/) as a backup mechanism that doesn't
require shutting down to do the backup and can restore to bare metal
including reconstructing the underlying raid/lvm/filesystems.
Clonezilla can work too, but you have to shut down for the save and it
doesn't do raid (but on the plus side it can handle windows
partitions).

> Patches are welcome. LVM is designed not to activate a partial VG
> unless the user specifies --partial. This is because for non-mirrored
> LVs activating without all PVs present would leave holes in devices.

Wait, so LVM doesn't know if the volume it is starting is complete or
not in the case of mirrors and --partial just blindly starts anyway?
 That's one of those things where you have to ask what they were
thinking.

-- 
   Les Mikesell
      lesmikesell at gmail.com