[libvirt-users] Create qcow2 v3 volumes via libvirt

[Gionatan Danti]

On 04/05/2018 10:26, Kashyap Chamarthy wrote:
> Yes, you still have to clean up external snapshot metadata manually, as
> the link below indicates.  Deleting external snapshots is a non-trivial
> problem.  For example, if you have a disk image chain like:
> 
>      [A] <-- [B] <-- [C] <-- [D]
>      
> Now if you no longer need image [B], what is the most efficient way to
> get rid of it?  Three possibilities:
> 
>    - Merge [B] into [A], and rewrite the backing chain of [C]
>      to point to [A].  Now can you discard image [B].
>    - Merge [A] into [B], call the new image [AB].  Now you can
>      discard [A].
>    - Merge [B] into [C], and rewrite the backing chain of [C] to point to
>      [A].  Now you can discard image [B].
>      
> It depends on how large each of the disk images are, and based on the
> size, merge / coalesce them accordingly, to arrive at the quickest
> solution.

True.

> 
> Note that existing commands (`virsh blockpull` and `virsh blockcommit`,
> which is relatively faster) will allow you handle it manually or script
> it -- which many people already do it. >
> A couple of references (that are also easily scriptable):
> 
>      http://wiki.libvirt.org/page/Live-merge-an-entire-disk-image-chain-including-current-active-disk
>      https://wiki.libvirt.org/page/Live-disk-backup-with-active-blockcommit
> 
>>> [1]
>>> https://www.redhat.com/archives/libvirt-users/2015-September/msg00037.html
>>
>> Any hope to get virsh external snapshot creation/deletion fixed?
> 
> I don't see any problem creation external snapshots (or more correctly:
> "overlays").  Deletion of external snapshots involves a bit more work,
> but it is scriptable as well.
> 

Reading old mailing list posts, I was under impression that some work 
was put to automatically and trasparently issue the best 
blockpull/blockcommit command. If not - fair enough ;)

Thanks.

-- 
Danti Gionatan
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