>>Can you post more details about your benchmark setup so that this can be >>reproduced? And does it reproduce with local files as well or only using >>NFS?
Sure, I have redone tests, here the results: (note that my netapp san have a nvram journal, so directio are as fast than buffered io) preallocated vs non preallocated have a ratio of 5/1 for local, and 10/1 for nfs. directio bench --------------- fio --filename=/dev/vdb --direct=1 -rw=randwrite --bs=4K --size=5G --iodepth=100 --group-reporting --name=file1 --ioengine=libaio buffered io bench ------------------ fio --filename=/dev/vdb --direct=1 -rw=randwrite --bs=4K --size=5G --iodepth=100 --group-reporting --name=file1 --ioengine=libaio results ------- local raw file --------------- cache=none, directio, 9000 iops cache=none, buffered io, 10000 iops local qcow2 preallocated -------------------------- cache=none, directio, 8000 iops cache=none, buffered io, 9000 iops local qcow2 non preallocated ----------------------------- cache=none, directio, 1400 iops cache=none, buffered io, 2000 iops nfs rawfile (netapp with nvram journal) ---------------------------------------- cache=none, directio, 15000 iops cache=none, buffered io, 15000 iops nfs qcow2 preallocated (netapp with nvram journal) ------------------- cache=none, directio, 12000 iops cache=none, buffered io, 12000 iops nfs qcow2 non preallocated (netapp with nvram journal) ----------------------------------------------------- cache=none, directio, 1500 iops cache=none, buffered io, 1500 iops Alexandre D e rumier Ingénieur Systèmes et Réseaux Fixe : 03 20 68 88 85 Fax : 03 20 68 90 88 45 Bvd du Général Leclerc 59100 Roubaix 12 rue Marivaux 75002 Paris ----- Mail original ----- De: "Kevin Wolf" <[email protected]> À: "Alexandre DERUMIER" <[email protected]> Cc: "Dietmar Maurer" <[email protected]>, [email protected] Envoyé: Vendredi 23 Novembre 2012 15:58:09 Objet: Re: [Qemu-devel] qcow2: slow internal snapshot creation Am 23.11.2012 15:17, schrieb Alexandre DERUMIER: >>> Preallocation doesn't matter much these days. > > I have done benchmark through nfs on a netapp san, (with directio), > > I got 300 iops without preallocation, and 6000 iops with preallocation .... This doesn't sound right, even for writethrough modes. Can you post more details about your benchmark setup so that this can be reproduced? And does it reproduce with local files as well or only using NFS? Kevin
