>>> Alexandre DERUMIER <aderumier@xxxxxxxxx> schrieb am Mittwoch, 31. August 2016 um 16:10: >> >eanwhile I tried to update the viostor driver within the vm (a W2k8) >>>but that >>>results in a bluescreen. > >>>When booting via recovery console and loading the new driver from an >>>actual >>>qemu driver iso the disks are all in writeback mode. >>>So maybe the cache mode depends on the iodriver within the machine. >>> >>>I'll see how to upgrade the driver without having a bluescreen >>>afterwards >>>(by having another reason to avoid that windows crap). > > Very old virtio drivers (don't remember, but it was some year ago), didn't > support flush/fua correctly. > https://bugzilla.redhat.com/show_bug.cgi?id=837324 > > So, it's quite possible that rbd_cache_writethrough_until_flush force > writethrough in this case. That makes sense. The time reference of the bugreport matches the driver version 61.63.103.3000 from 03.07.2012 distributed with virtio-win-0.1-30.iso from Fedora. Thank you. Regards > > ----- Mail original ----- > De: "Steffen Weißgerber" <WeissgerberS@xxxxxxx> > À: "ceph-users" <ceph-users@xxxxxxxxxxxxxx>, lc@xxxxxxxxxxxxxxxxx > Envoyé: Mercredi 31 Août 2016 15:43:17 > Objet: Antw: Re: rbd cache mode with qemu > >>>> Loris Cuoghi <lc@xxxxxxxxxxxxxxxxx> schrieb am Dienstag, 30. August > 2016 um > 16:34: >> Hello, >> > > Hi Loris, > > thank you for your answer. > >> Le 30/08/2016 à 14:08, Steffen Weißgerber a écrit : >>> Hello, >>> >>> after correcting the configuration for different qemu vm's with rbd > disks >>> (we removed the cache=writethrough option to have the default >>> writeback mode) we have a strange behaviour after restarting the > vm's. >>> >>> For most of them the cache mode is now writeback as expected. But > some >>> neverthless use the disks in writethrough mode (at least an 'info > block' >>> reports that on the qemu monitor). This does also not change when >>> configuring cache=writeback explicitly. >>> >>> On our 6 node KVM Cluster we have the same behaviour for the > problematic >>> vm's on all hosts which are configured equally with qemu 2.5.1, ceph > 0.94.7 >>> and kernel 4.4.6. >>> >>> The ceph cluster has version 0.94.6. >>> >>> For me it seems to be a problem specific to the rbd's. Is there a > way to >>> check the cache behaviour of a single rbd? >> >> To my knowledge, there is not such a thing as an RBD's cache mode. >> >> The librbd cache exists in the client's memory, not on the Ceph >> cluster's hosts. Its configuration is to be put in the ceph >> configuration file, on each client host. >> > > Yes, that's what I think also but my guess was that the client cache > behaviour > is somehow controlled by the communication between librbd on the client > and > the ceph cluster. > >> Setting QEMU's disk cache mode to "writeback" informs the guest's OS > >> that it needs to explicitly flush dirty data to persistent storage > when >> needed. > > Meanwhile I tried to update the viostor driver within the vm (a W2k8) > but that > results in a bluescreen. > > When booting via recovery console and loading the new driver from an > actual > qemu driver iso the disks are all in writeback mode. > So maybe the cache mode depends on the iodriver within the machine. > > I'll see how to upgrade the driver without having a bluescreen > afterwards > (by having another reason to avoid that windows crap). > >> >>> >>> Regards >>> >>> Steffen >>> >>> > > Regards > >>> >> _______________________________________________ >> ceph-users mailing list >> ceph-users@xxxxxxxxxxxxxx >> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > -- > Klinik-Service Neubrandenburg GmbH > Allendestr. 30, 17036 Neubrandenburg > Amtsgericht Neubrandenburg, HRB 2457 > Geschaeftsfuehrerin: Gudrun Kappich > _______________________________________________ > ceph-users mailing list > ceph-users@xxxxxxxxxxxxxx > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com -- Klinik-Service Neubrandenburg GmbH Allendestr. 30, 17036 Neubrandenburg Amtsgericht Neubrandenburg, HRB 2457 Geschaeftsfuehrerin: Gudrun Kappich _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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