Hello Webert, On Fri, May 18, 2018 at 1:10 PM, Webert de Souza Lima <webert.b...@gmail.com> wrote: > Hi, > > We're migrating from a Jewel / filestore based cephfs archicture to a > Luminous / buestore based one. > > One MUST HAVE is multiple Active MDS daemons. I'm still lacking knowledge of > how it actually works. > After reading the docs and ML we learned that they work by sort of dividing > the responsibilities, each with his own and only directory subtree. (please > correct me if I'm wrong).
Each MDS may have multiple subtrees they are authoritative for. Each MDS may also replicate metadata from another MDS as a form of load balancing. > Question 1: I'd like to know if it is viable to have 4 MDS daemons, being 3 > Active and 1 Standby (or Standby-Replay if that's still possible with > multi-mds). standby-replay daemons are not available to take over for ranks other than the one it follows. So, you would want to have a standby-replay daemon for each rank or just have normal standbys. It will likely depend on the size of your MDS (cache size) and available hardware. > Basically, what we have is 2 subtrees used by dovecot: INDEX and MAIL. > Their tree is almost identical but INDEX stores all dovecot metadata with > heavy IO going on and MAIL stores actual email files, with much more writes > than reads. > > I don't know by now which one could bottleneck the MDS servers most so I > wonder if I can take metrics on MDS usage per pool when it's deployed. > Question 2: If the metadata workloads are very different I wonder if I can > isolate them, like pinning MDS servers X and Y to one of the directories. It's best if y ou see if the normal balancer (especially in v12.2.6 [1]) can handle the load for you without trying to micromanage things via pins. You can use pinning to isolate metadata load from other ranks as a stop-gap measure. [1] https://github.com/ceph/ceph/pull/21412 -- Patrick Donnelly _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
