Re: [libvirt-users] Reintroduce "allocate entire disk" checkbox on virt-manager
On 06/19/2018 07:06 PM, Gionatan Danti wrote:
Il 19-06-2018 22:16 Cole Robinson ha scritto:
> Sorry, I misunderstood. You can still achieve what you want but it's
> more clicks: new vm, manage storage, add volume, and select raw volume
> with whatever capacity you want but with 0 allocation.
Sure, but the automatic disk creation is very handy and much less error
prone.
As it is now, if using a fallocate-less filesystem (eg: ZFS) and *not*
selecting to create a custom disk, you risk waiting minutes or hours for
libvirt to fully allocate the image by writing 0s to the disk file. This
can wreck havok on SSDs and other eundurance-limited medium.
> qcow2 is the default for virt-manager because it enables features like
> snapshots out of the box. The main motivation I have largely heard for
> wanting raw over qcow2 is performance, but then using sparse raw
> actually makes raw less performant, so it's kind of a weird middle
> ground. For that reason I don't think it warrants adding back the
> checkbox to the new VM UI since I think it's a fairly obscure use case,
> and it can be achieved through the 'manage storage' wizard albeit with
> more clicks
>
> - Cole
On CoW filesystems, sparse RAW files are faster then Qcow2 ones.
Moreover, avoiding double CoW is important for SSDs (which have limited
lifespan). Even on XFS, sparse RAW files should be faster in the long
run than Qcow2 files, due to no weird limitation on L2 chunk cache size.
I found the checkbox quite self-explanatory and very handy. Any chances
to reconsider your decision?
I see it as another test case and larger UI surface in the common path
for something that will save clicks for a corner case. I still don't see
it asworth exposing in the UI.
- Cole