On Wed, Nov 25, 2015 at 12:30 AM, Mike Miller <millermike287@xxxxxxxxx> wrote: > Hi Greg, > > thanks very much. This is clear to me now. > > As for 'MDS cluster', I thought that this was not recommended at this stage? > I would very much like to have a number >1 of MDS in my cluster as this > would probably help very much to balance the load. But I am afraid what > everybody says about stability issues. > > Is more than one MDS considered stable enough with hammer? You're correct, it's unfortunately not recommended yet. :( -Greg > > Thanks and regards, > > Mike > > > On 11/25/15 12:51 PM, Gregory Farnum wrote: >> >> On Tue, Nov 24, 2015 at 10:26 PM, Mike Miller <millermike287@xxxxxxxxx> >> wrote: >>> >>> Hi, >>> >>> in my cluster with 16 OSD daemons and more than 20 million files on >>> cephfs, >>> the memory usage on MDS is around 16 GB. It seems that 'mds cache size' >>> has >>> no real influence on the memory usage of the MDS. >>> >>> Is there a formula that relates 'mds cache size' directly to memory >>> consumption on the MDS? >> >> >> The dominant factor should be the number of inodes in cache, although >> there are other things too. Depending on version I think it was ~2KB >> of memory for each inode+dentry at last count. >> >>> In the documentation (and other posts on the mailing list) it is said >>> that >>> the MDS needs 1 GB per daemon. I am observing that the MDS uses almost >>> exactly 1 GB per OSD daemon (I have 16 OSD and 16 GB memory usage on the >>> MDS). Is this the correct formula? >>> >>> Or is it 1 GB per MDS daemon? >> >> >> It's got nothing to do with the number of OSDs. I'm not sure where 1GB >> per MDS came from, although you can certainly run a reasonable >> low-intensity cluster on that. >> >>> >>> In my case, the standard 'mds cache size 100000' makes MDS crash and/or >>> the >>> cephfs is unresponsive. Larger values for 'mds cache size' seem to work >>> really well. >> >> >> Right. You need the total cache size of your MDS "cluster" (which is >> really just 1) to be larger than your working set size or you'll have >> trouble. Similarly if you have any individual directories which are a >> significant portion of your total cache it might cause issues. >> -Greg >> > _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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