On Tue, Jan 22, 2019 at 10:49 AM Albert Yue <transuranium....@gmail.com> wrote: > > Hi Yan Zheng, > > In your opinion, can we resolve this issue by move MDS to a 512GB or 1TB > memory machine? >
The problem is from client side, especially clients with large memory. I don't think enlarge mds cache size is good idea. you can periodically check periodically each kernel clients' /sys/kernel/debug/ceph/xxx/caps. run 'echo 2 >/proc/sys/vm/drop_caches' if a client used too many caps (for example 10k), > On Mon, Jan 21, 2019 at 10:49 PM Yan, Zheng <uker...@gmail.com> wrote: >> >> On Mon, Jan 21, 2019 at 11:16 AM Albert Yue <transuranium....@gmail.com> >> wrote: >> > >> > Dear Ceph Users, >> > >> > We have set up a cephFS cluster with 6 osd machines, each with 16 8TB >> > harddisk. Ceph version is luminous 12.2.5. We created one data pool with >> > these hard disks and created another meta data pool with 3 ssd. We created >> > a MDS with 65GB cache size. >> > >> > But our users are keep complaining that cephFS is too slow. What we >> > observed is cephFS is fast when we switch to a new MDS instance, once the >> > cache fills up (which will happen very fast), client became very slow when >> > performing some basic filesystem operation such as `ls`. >> > >> >> It seems that clients hold lots of unused inodes their icache, which >> prevent mds from trimming corresponding objects from its cache. mimic >> has command "ceph daemon mds.x cache drop" to ask client to drop its >> cache. I'm also working on a patch that make kclient client release >> unused inodes. >> >> For luminous, there is not much we can do, except periodically run >> "echo 2 > /proc/sys/vm/drop_caches" on each client. >> >> >> > What we know is our user are putting lots of small files into the cephFS, >> > now there are around 560 Million files. We didn't see high CPU wait on MDS >> > instance and meta data pool just used around 200MB space. >> > >> > My question is, what is the relationship between the metadata pool and >> > MDS? Is this performance issue caused by the hardware behind meta data >> > pool? Why the meta data pool only used 200MB space, and we saw 3k iops on >> > each of these three ssds, why can't MDS cache all these 200MB into memory? >> > >> > Thanks very much! >> > >> > >> > Best Regards, >> > >> > Albert >> > >> > _______________________________________________ >> > ceph-users mailing list >> > ceph-users@lists.ceph.com >> > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
