>>In the short-term, you can remove the "rbd cache" setting from your ceph.conf That's not true, you need to remove the ceph.conf file. Removing rbd_cache is not enough or default rbd_cache=false will apply. I have done tests, here the result matrix host ceph.conf : no rbd_cache : guest cache=writeback : result : nocache (wrong) host ceph.conf : rbd_cache=false : guest cache=writeback : result : nocache (wrong) host ceph.conf : rbd_cache=true : guest cache=writeback : result : cache host ceph.conf : no rbd_cache : guest cache=none : result : nocache host ceph.conf : rbd_cache=false : guest cache=none : result : no cache host ceph.conf : rbd_cache=true : guest cache=none : result : cache (wrong) ----- Mail original ----- De: "Jason Dillaman" <dillaman@xxxxxxxxxx> À: "Andrey Korolyov" <andrey@xxxxxxx> Cc: "Josh Durgin" <jdurgin@xxxxxxxxxx>, "aderumier" <aderumier@xxxxxxxxx>, "ceph-users" <ceph-users@xxxxxxxxxxxxxx> Envoyé: Lundi 8 Juin 2015 22:29:10 Objet: Re: rbd cache + libvirt > On Mon, Jun 8, 2015 at 10:43 PM, Josh Durgin <jdurgin@xxxxxxxxxx> wrote: > > On 06/08/2015 11:19 AM, Alexandre DERUMIER wrote: > >> > >> Hi, > >>>> > >>>> looking at the latest version of QEMU, > >> > >> > >> It's seem that it's was already this behaviour since the add of rbd_cache > >> parsing in rbd.c by josh in 2012 > >> > >> > >> http://git.qemu.org/?p=qemu.git;a=blobdiff;f=block/rbd.c;h=eebc3344620058322bb53ba8376af4a82388d277;hp=1280d66d3ca73e552642d7a60743a0e2ce05f664;hb=b11f38fcdf837c6ba1d4287b1c685eb3ae5351a8;hpb=166acf546f476d3594a1c1746dc265f1984c5c85 > >> > >> > >> I'll do tests on my side tomorrow to be sure. > > > > > > It seems like we should switch the order so ceph.conf is overridden by > > qemu's cache settings. I don't remember a good reason to have it the > > other way around. > > > > Josh > > > > Erm, doesn`t this code *already* represent the right priorities? > Cache=none setting should set a BDRV_O_NOCACHE which is effectively > disabling cache in a mentioned snippet. > Yes, the override is applied (correctly) based upon your QEMU cache settings. However, it then reads your configuration file and re-applies the "rbd_cache" setting based upon what is in the file (if it exists). So in the case where a configuration file has "rbd cache = true", the override of "rbd cache = false" derived from your QEMU cache setting would get wiped out. The long term solution would be to, as Josh noted, switch the order (so long as there wasn't a use-case for applying values in this order). In the short-term, you can remove the "rbd cache" setting from your ceph.conf so that QEMU controls it (i.e. it cannot get overridden when reading the configuration file) or use a different ceph.conf for a drive which requires different cache settings from the default configuration's settings. Jason _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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