> On 20 Oct 2015, at 10:34, Luis Periquito <periqu...@gmail.com> wrote: > > On Tue, Oct 20, 2015 at 3:26 AM, Haomai Wang <haomaiw...@gmail.com> wrote: >> The fact is that journal could help a lot for rbd use cases, >> especially for small ios. I don' t think it will be bottleneck. If we >> just want to reduce double write, it doesn't solve any performance >> problem. >>
Yes, in theory journal sounds like an excellent idea, but one would expect to have performance somewhere between an SSD journal device and a HDD filestore when trying that use case. In practice, you get close to good HDD performance for small writes, like databases do. The complexity just needs to drop if it has to compete with anything... > > One trick I've been using in my ceph clusters is hiding a slow write > backend behind a fast journal device. The write performance will be of > the fast (and small) journal device. This only helps on write, but it > can make a huge difference. > Do you mean an external filesystem journal? What filesystem? ext4/xfs? I tried that on a physical machine and it worked wonders with both of them, even though data wasn't journaled and hit the platters - I don't yet understand how that was possible but the benchmark just flew. Jan > I've even made some tests showing (within 10%, RBD and S3) that the > backend device doesn't matter and the write performance is exactly the > same as that of the journal device fronting all the writes. _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
