Am 23.11.2012 15:03, schrieb Alexandre DERUMIER: > performance is also reduced when snapshot exist. (like if they are no > preallocated metadatas)
Preallocation doesn't matter much these days. > see initial git commit > > http://git.qemu.org/?p=qemu.git;a=commit;h=a35e1c177debb01240243bd656caca302410d38c > "qcow2: Metadata preallocation > > This introduces a qemu-img create option for qcow2 which allows the metadata > to > be preallocated, i.e. clusters are reserved in the refcount table and L1/L2 > tables, but no data is written to them. Metadata is quite small, so this > happens in almost no time. > > Especially with qcow2 on virtio this helps to gain a bit of performance during > the initial writes. However, as soon as create a snapshot, we're back to the > normal slow speed, obviously. So this isn't the real fix, but kind of a cheat > while we're still having trouble with qcow2 on virtio." This is a commit message from 2009 that already says that this wasn't the final solution. Kevin
