On Sat, Jun 30, 2012 at 8:21 PM, Vladimir Bashkirtsev <vladimir@xxxxxxxxxxxxxxx> wrote: > On 01/07/12 11:59, Josh Durgin wrote: >> >> On 06/30/2012 07:15 PM, Vladimir Bashkirtsev wrote: >>> >>> On 01/07/12 10:47, Josh Durgin wrote: >>>> >>>> On 06/30/2012 05:42 PM, Vladimir Bashkirtsev wrote: >>>>> >>>>> Dear all, >>>>> >>>>> Currently I testing KVMs running on ceph and particularly testing >>>>> recent >>>>> cache feature. Performance is of course vastly improved but still have >>>>> occasional KVM hold ups - not sure who is at blame ceph of KVM. But I >>>>> will deal with it later. Right now I've got myself a question which I >>>>> could not get answered myself: if I do live migration of KVM while >>>>> there >>>>> some uncommitted data in ceph cache will this cache be committed prior >>>>> cut-over to another host? Reading through the list I've got an >>>>> impression that it may be left uncommitted and thus it may cause data >>>>> corruption. I just would like a simple confirmation if code which >>>>> commits cache on cut-over to new host does exist and no data corruption >>>>> due to RBD cache+live migration should happen. >>>>> >>>>> Regards, >>>>> Vladimir >>>> >>>> >>>> QEMU does a flush on all the disks when it stops the guest on the >>>> original host, so there will be no uncommitted data in the cache. >>>> >>>> Josh >>> >>> Thank you for quick and precise answer. Now when I actually attempted to >>> live migrate ceph based VM I get: >>> >>> Unable to migrate guest: Invalid relative path >>> 'rbd/mail.logics.net.au:rbd_cache=true': Invalid argument >>> >>> I guess KVM does not like having :rbd_cache=true (migration works >>> without it). I know that it is most likely KVM problem but still decided >>> to ask here in case if you know about it. Any ideas how to fix it? >>> >>> Regards, >>> Vladimir >> >> >> Is the destination librbd older and not supporting the cache option? >> >> Migrating with rbd_cache=true and other options specified like that >> worked in my testing. >> >> Josh > > Both installations are the same: > qemu 1.0.17 > ceph 0.47.3 > libvirt 0.9.12 > > I have googled around and found that if I call migration with --unsafe > option then it should go. And indeed: it works. Apparently this check > introduced in libvirt 0.9.12 . Did quick downgrade to libvirt 0.9.11 and no > problems migrating. Have we checked if the live migrate actually does do the cache flushes when you use the unsafe flag? That worries me a little! In either case, I created a bug so we can try and make QEMU play nice: http://tracker.newdream.net/issues/2685 -Greg -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
