Right now, no. We could add a minimum read size to librbd when caching is enabled... that would not be particularly difficult.
sage On Fri, 13 Jun 2014, Ke-fei Lin wrote: > 2014-06-13 22:04 GMT+08:00 Andrey Korolyov <and...@xdel.ru>: > > > > On Fri, Jun 13, 2014 at 5:50 PM, Ke-fei Lin <k...@kfei.net> wrote: > > > Thanks, Andrey. > > > > > > I tried `virsh domblkstat <vm> hda` (only this VM in whole cluster) and > got > > > these values: > > > > > > hda rd_req 70682 > > > hda rd_bytes 229894656 > > > hda wr_req 1067 > > > hda wr_bytes 12645888 > > > hda flush_operations 0 > > > > > > (These values became stable after ~2 mins) > > > > > > While the output of `ceph -w` is attached at: > http://pastebin.com/Uhdj9drV > > > > > > Any advices? > > > > > > Thanks, poor man`s analysis shows that it can be true - assuming > > median heartbeat value as 1.2s, overall read ops are about 40k, which > > is close enough to what qemu stats saying, regarding floating > > heartbeat interval. Because ceph -w never had such value as a precise > > measurement tool, I may suggest to measure block stats difference on > > smaller intervals, about 1s or so, and compare values then. By the > > way, what driver do you use in qemu for a block device? > > OK, this time I capture the blkstat difference in a smaller interval (less > than 1s). > And a simple calculation gives me some result: > > (19531264-19209216)/(38147-37518) = 512 > ... > (20158976-19531264)/(39373-38147) = 512 > > Which means in the beginning of boot phase, every read request from VM is > just *512 byte*. > Maybe this is why `ceph -w` shows me every operation is about 1KB (in my > first post)? > > So seems this is the inherent problem of Windows VM, but can I do something > in my Ceph > cluster's configuration to improve this? > > By the way the related part of my VM definition are: > > <emulator>/usr/bin/kvm</emulator> > <disk type='network' device='disk'> > <driver name='qemu' type='rbd' cache='writeback'/> > <source protocol='rbd' name='libvirt-pool/test-rbd-1'> > <host name='10.0.0.5' port='6789'/> > </source> > <target dev='hda' bus='ide'/> > <address type='drive' controller='0' bus='0' unit='0'/> > </disk> > > Thanks. > >
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