That big fat warning was related to the note under your second quote: "Note: Prior to QEMU v2.4.0, if you explicitly set RBD Cache settings in the Ceph configuration file, your Ceph settings override the QEMU cache settings."
Short story long, starting with QEMU v2.4.0, your QEMU cache settings 100% control/override your librbd cache settings to prevent such situations. On Fri, Jan 19, 2018 at 7:48 AM, Wolfgang Lendl <wolfgang.le...@meduniwien.ac.at> wrote: > hi, > > I'm a bit confused after reading the official ceph docu regarding QEMU and > rbd caching. > > http://docs.ceph.com/docs/master/rbd/qemu-rbd/?highlight=qemu > > there's a big fat warning: > > "Important: If you set rbd_cache=true, you must set cache=writeback or risk > data loss. Without cache=writeback, QEMU will not send flush requests to > librbd. If QEMU exits uncleanly in this configuration, filesystems on top of > rbd can be corrupted." > > two sections below you can find the following: > > "QEMU’s cache settings override Ceph’s cache settings (including settings > that are explicitly set in the Ceph configuration file)." > > > I find these two statements contradicting and looking for the truth - or did > i miss something? > > ceph/librbd: 12.2 > qemu/kvm: 2.9.0 > > > br wolfgang > > > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > -- Jason _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
