[libvirt-users] Reintroduce "allocate entire disk" checkbox on virt-manager

[Gionatan Danti]

Il 19-06-2018 20:14 Cole Robinson ha scritto:
> If you change the disk image format from qcow2 to raw in
> Edit->Preferences, then new disk images are set to fully allocated raw.
> Check the image details with 'qemu-img info $filename' to confirm. So I
> think by default we are doing what you want?
> 
> - Cole

Er, the point is that I would really like to have a *sparse* RAW image 
file. On older virt-manager, unchecking "allocate entire disk" was what 
I normally used. Auto-allocating all disk space without a mean to avoid 
that has two main drawbacks:
- you can't have sparse/thin volumes;
- allocating on a fallocate-less filesystem is excruciatingly slow and 
cause of unneeded wear on SSDs.

Why using a sparse RAW image rather than a Qcow2 image? Basically:
- RAW disks are easier to handle/inspect in case something goes wrong;
- avoid double CoW on CoW-enabled filesystems (eg: ZFS, btrfs);
- better performance (no Qcow2 L2 chunk cache range, etc).

It is worth nothing that oVirt (and RHEV) uses (sparse or allocated, 
based on user selection) base RAW files with eventual Qcow2 overlays for 
snapshots.

Thanks.

-- 
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti at assyoma.it - info at assyoma.it
GPG public key ID: FF5F32A8