On Wed, Jan 23, 2019 at 10:02 AM Albert Yue <transuranium....@gmail.com> wrote: > > But with enough memory on MDS, I can just cache all metadata into memory. > Right now there are around 500GB metadata in the ssd. So this is not enough? >
mds needs to tracking lots of extra information for each object. For 500G metadata, mds may need 1T or more memory. > On Tue, Jan 22, 2019 at 5:48 PM Yan, Zheng <uker...@gmail.com> wrote: >> >> 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
