On Wed, Sep 16, 2015 at 11:56 AM, Corin Langosch <corin.lango...@netskin.com> wrote: > Hi guys, > > afaik rbd always splits the image into chunks of size 2^order (2^22 = 4MB by > default). What's the benefit of specifying > the feature flag "STRIPINGV2"? I couldn't find any documenation about it > except > http://ceph.com/docs/master/man/8/rbd/#striping which doesn't explain the > benefits (or I just don't get it). Better docs > in this area would be greatm, so I created an issue for that: > http://tracker.ceph.com/issues/13123
Briefly, if you do a lot of small direct IOs (for instance, a database journal) then striping lets you send each sequential write to a separate object. This means they don't pile up behind each other grabbing write locks and can complete in parallel. Striping them instead of just having small block-sized objects means the objects are still of a reasonable size for RADOS. > > I also noticed the rbd client (0.94.3) ignores the striping feature on image > creation, I created issue > http://tracker.ceph.com/issues/13122 for that. It is really a bug or does it > mean stripingv2 is going away and should > not be used? I *think* that's just because the features are only filled in if they're in use (the kernel doesn't/didn't support striping, despite supporting other V2 image features) and required to understand the image, but maybe I'm misunderstanding you or forgetting how the RBD team set things up. -Greg _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
