On Thu, Mar 19, 2015 at 4:46 AM, Matthijs Möhlmann <matthijs@xxxxxxxxxxxx> wrote: > > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Hi, > > - From the documentation: > > Cache Tier readonly: > > Read-only Mode: When admins configure tiers with readonly mode, Ceph > clients write data to the backing tier. On read, Ceph copies the > requested object(s) from the backing tier to the cache tier. Stale > objects get removed from the cache tier based on the defined policy. > This approach is ideal for immutable data (e.g., presenting > pictures/videos on a social network, DNA data, X-Ray imaging, etc.), > because reading data from a cache pool that might contain out-of-date > data provides weak consistency. Do not use readonly mode for mutable data. > > Does this mean that when a client (xen / kvm with a RBD volume) writes > some data that the OSD does not mark the readonly cache dirty? Yes, exactly. Reads are directed to the cache but writes go directly to the base tier, and there's no attempt at communication about the changed objects. -Greg _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
 |