>>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. ----- 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 _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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