On Wed, Jan 9, 2013 at 5:32 PM, Eric Blake <ebl...@redhat.com> wrote: > On 01/09/2013 09:16 AM, Stefan Hajnoczi wrote: > >>> I.6) max refcount reached >>> The L2 hash block of the cluster is written in order to remember at next >>> startup >>> that it must not be used anymore for deduplication. The hash is dropped >>> from the >>> gtrees. >> >> Interesting case. This means you can no longer take snapshots >> containing this cluster because we cannot track references :(. >> >> Worst case: guest fills the disk with the same 4 KB data (e.g. >> zeroes). There is only a single data cluster but the refcount is >> maxed out. Now it is not possible to take a snapshot. > > Except that a sector of all zeroes should be represented as a hole,
QEMU doesn't scan data buffers for all zero by default. Stefan
