Migrate to a bigger disk possible?

[Peter Krempa]

On Sat, Apr 25, 2020 at 16:40:35 +0200, Paul van der Vlis wrote:
> Op 25-04-2020 om 16:00 schreef Paul van der Vlis:
> > Hello,
> > 
> > I have a qcow2 disk what needs to become increased.
> > 
> > I don't have space on the location where it is now to have it two time,
> > so I want to live-migrate it to another host.
> > 
> > On the other host I have to create a qcow2 disk before I can migrate.
> > 
> > What would happen when I would create there a bigger qcow2 disk then the
> > original one?  Can I resize the filesystem after the migration?
> 
> Not sure why, but I thought it's not possible to encrease qcow2 disks
> without copying the disk. But now I find many manuals what say it's no
> problem. Sorry...

It definitely is possible. There are multiple options though and I
didn't quite get which one is your case:

1) QCOW2 image is too small but theres unused space on the filesystem
   where the image is stored:

   - live:
   The image can be resized live via 'virsh blockresize'. You then must
   modify the partitions and enlarge filesystem.

   - offline:
   'virt-resize' tool from the libguestfs package can be used to do it
   offline and it should be able to resize your partitions and
   filesystem as well.


2) QCOW2 is too small and there isn't enough space on the filesystem,
   but there's enough space on a different filesystem on the same host:

   - live:
   'virsh blockcopy' can be used to copy the existing image to the new
   filesystem while the VM is running and then switch to it. You can
   then use same steps as in 1) to resize the filesystem.

   - offline
   copying the image and using the steps from 1) is the best bet here

3) QCOW2 is too small and there isn't enough storage on the same host,
   but there is a different host where I want to run it.

   -live
   You can use VM live migration to migrate the VM to the other host and
   then enlarge the disk using steps in 1). Please refer to the docs of
   live migration.

   - offline
   Copying the image and VM XML config is the best bet here.