On 10/26/2011 10:48 AM, Markus Armbruster wrote:
Sector size is a device property.
If the user asks for a 4K sector disk, and the backend can't support
that, we need to reject the configuration. Just like we reject
read-only backends for read/write disks.
Isn't it the other way round, i.e. the user asks for a 512-byte sector
disk (i.e. the default) with cache=none but the disk has 4k sectors?
We're basically saying "choose between NFS and migration if you have 4k
sector disks but your guest doesn't support them". Understandable
perhaps, but not exactly kind, and virtualization is also about
shielding from this kind of hardware dependency even at the cost of
performance. QEMU should just warn about performance degradations,
erroring out would be a policy decision that should be up to management.
It's okay to default device properties to some backend-dependent value,
if that improves usability.
On the other hand, not all guests support 4k-sectors properly.
Paolo
