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Re: moving LVM logical volumes to new disks

Don Armstrong <don@debian.org> writes:

> On Wed, 12 Nov 2014, lee wrote:
>> what's the best way to move existing logical volumes or a whole volume
>> group to new disks?
>> The target disks cannot be installed at the same time as the source
>> disks.  I will have to make some sort of copy over the network to
>> another machine, remove the old disks, install the new disks and put the
>> copy in place.
>> The LVs contain VMs. The VMs can be shut down during the migration.
>> It's not possible to make snapshots because the VG is full.
>> New disks will be 6x1TB RAID-5, old ones are 2x74GB RAID-1 on a
>> ServeRaid 8k. No more than 6 discs can be installed at the same time.
> You can remove one of the RAID-1 drives, install 5 of the 1T drives, and
> start both raids in degraded mode temporarily. Once you've done that,
> add the new PVs to the VG, and pvmove.
> Alternatively, you can start with three drives in raid-5, and then grow
> the array out to the additional three drives, once you've done the
> migration, or have two different raid-5 arrays in the same vg.
> Alternatively, you can use an external enclosure to house the RAID1 or
> RAID5 temporarily. USB is slow, but workable.

Yes, I thought about something like this.  I'm not sure whether I can
actually grow the RAID-5.  I could create the new RAID-5 with 6 disks
and then remove one to run both arrays in degraded mode to copy things

However, I currently have dom0 on a non-LVM partition, and I want to
make a single LVM partition from the new RIAD-5 with several LVs.  The
largest LV will be for data.  I want to have more room for VMs, too, and
I want to be able to increase the size of the existing LVs --- either in
the future or while I am at it.

I want to convert dom0 to a LV, and I'm not sure whether it's better to
re-install dom0 on LV or to copy and convert the existing one somehow.

I'm also not sure what limits copying with dd would introduce.  I might
be better off making copies of everything over the network --- with the
added benefit of having a backup which I currently don't have --- and
then copying everything back with something like 'cp -a'.  Using 'cp -a'
worked fine in the past, and I was able to boot a rescue system to
install grub.

I've never done that with VMs in LVs, though.  When I boot a rescue
system, can I still install grub in each of the LVs?

I also have a spare 1TB disk which I can use in another machine
to make the backups to.

Again we must be afraid of speaking of daemons for fear that daemons
might swallow us.  Finally, this fear has become reasonable.

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