On 29/09/2016 12:39, Kevin Wolf wrote: >> > >> > Because there is another check of pass-discard-request value in >> > update_refcount: >> > >> > if (refcount == 0 && s->discard_passthrough[type]) { >> > update_refcount_discard(bs, cluster_offset, s->cluster_size); >> > } > What I mean is that in the second case, you're still uselessly > deallocating the cluster on the qcow2 level while you can't reclaim it > on the filesystem level. So it would be better to leave it allocated in > qcow2, too, so that you don't get an expensive reallocation the next > time you write to it.
But if you do a qemu-img convert, the deallocated cluster wouldn't be in the destination. Paolo