Skipping the bdrv_flush() in update_cluster_refcount() gives a huge speed-up from over 3 minutes down to <1 second. I think Kevin already discovered this in the past.
Now we need to figure out how to safely perform the updates without flushing after each L2 table refcount increment. -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1126369 Title: qemu-img snapshot -c is unreasonably slow Status in QEMU: New Bug description: Something fishy is going on with qcow2 internal snapshot creation times. I don't know if this is a regression because I haven't used internal snapshots in the past. QEMU 1.4-rc2: $ qemu-img create -f qcow2 test.qcow2 -o size=50G,preallocation=metadata $ time qemu-img snapshot -c new test.qcow2 real 3m39.147s user 0m10.748s sys 0m26.165s (This is on an SSD) I expect snapshot creation to take under 1 second. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1126369/+subscriptions
