On Sun, Mar 25, 2018 at 08:05:14PM +0000, Nir Soffer wrote:
> When using the sdk, you can select both the image format and sparse, so you
> can create invalid combinations. oVirt selects the allocation for you.
>
> storage type  image format  sparse | allocation      creating
> -----------------------------------|--------------------------------------------------------
> file          qcow2         true   | thin           sparse file of image
> size bytes
> file          raw           false  | preallocated   preallocated file of
> provisioned_size bytes
> file          raw           true   | thin           sparse file of
> provisioned_size
> bytes
> file          qcow2         false  | -              unsupported
> block         qcow2         true   | thin           logical volume of
> initial_size bytes
> block         raw           false  | preallocated   logical volume of
> provisioned_size bytes
> block         qcow2         false  | -              unsupported
> block         raw           true   | -              unsupported
>
> The only case when selecting the sparse value is useful is raw file
> on file based storage domain, allowing creation of sparse or preallocated
> disk.

I don't think this is true.  Both LVs (lvmthin) and SAN LUNs can
support sparse allocation meaningfully.