On Fri, Jun 3, 2016 at 10:43 PM, Jan Schermer <jan@xxxxxxxxxxx> wrote: > I'd be worried about it getting "fast" all of sudden. Test crash > consistency. > If you test something like file creation you should be able to estimate if > it should be that fast. (So it should be some fraction of theoretical IOPS > on the drives/backing rbd device...) Sudden "fast" is because MDS flushes its journal more frequently. There is no risk of metadata/data loss. Yan, Zheng > > If it's too fast then maybe the "sync" isn't working properly... > > Jan > > On 03 Jun 2016, at 16:26, David <dclistslinux@xxxxxxxxx> wrote: > > Zheng, thanks for looking into this, it makes sense although strangely I've > set up a new nfs server (different hardware, same OS, Kernel etc.) and I'm > unable to recreate the issue. I'm no longer getting the delay, the nfs > export is still using sync. I'm now comparing the servers to see what's > different on the original server. Apologies if I've wasted your time on > this! > > Jan, I did some more testing with Fuse on the original server and I was > seeing the same issue, yes I was testing from the nfs client. As above I > think there was something weird with that original server. Noted on sync vs > async, I plan on sticking with sync. > > On Fri, Jun 3, 2016 at 5:03 AM, Yan, Zheng <ukernel@xxxxxxxxx> wrote: >> >> On Mon, May 30, 2016 at 10:29 PM, David <dclistslinux@xxxxxxxxx> wrote: >> > Hi All >> > >> > I'm having an issue with slow writes over NFS (v3) when cephfs is >> > mounted >> > with the kernel driver. Writing a single 4K file from the NFS client is >> > taking 3 - 4 seconds, however a 4K write (with sync) into the same >> > folder on >> > the server is fast as you would expect. When mounted with ceph-fuse, I >> > don't >> > get this issue on the NFS client. >> > >> > Test environment is a small cluster with a single MON and single MDS, >> > all >> > running 10.2.1, CephFS metadata is an ssd pool, data is on spinners. The >> > NFS >> > server is CentOS 7, I've tested with the current shipped kernel (3.10), >> > ELrepo 4.4 and ELrepo 4.6. >> > >> > More info: >> > >> > With the kernel driver, I mount the filesystem with "-o >> > name=admin,secret" >> > >> > I've exported a folder with the following options: >> > >> > *(rw,root_squash,sync,wdelay,no_subtree_check,fsid=1244,sec=1) >> > >> > I then mount the folder on a CentOS 6 client with the following options >> > (all >> > default): >> > >> > >> > rw,relatime,vers=3,rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=192.168.3.231,mountvers=3,mountport=597,mountproto=udp,local_lock=none >> > >> > A small 4k write is taking 3 - 4 secs: >> > >> > # time dd if=/dev/zero of=testfile bs=4k count=1 >> > 1+0 records in >> > 1+0 records out >> > 4096 bytes (4.1 kB) copied, 3.59678 s, 1.1 kB/s >> > >> > real 0m3.624s >> > user 0m0.000s >> > sys 0m0.001s >> > >> > But a sync write on the sever directly into the same folder is fast >> > (this is >> > with the kernel driver): >> > >> > # time dd if=/dev/zero of=testfile2 bs=4k count=1 conv=fdatasync >> > 1+0 records in >> > 1+0 records out >> > 4096 bytes (4.1 kB) copied, 0.0121925 s, 336 kB/s >> >> >> Your nfs export has sync option. 'dd if=/dev/zero of=testfile bs=4k >> count=1' on nfs client is equivalent to 'dd if=/dev/zero of=testfile >> bs=4k count=1 conv=fsync' on cephfs. The reason that sync metadata >> operation takes 3~4 seconds is that the MDS flushes its journal every >> 5 seconds. Adding async option to nfs export can avoid this delay. >> >> > >> > real 0m0.015s >> > user 0m0.000s >> > sys 0m0.002s >> > >> > If I mount cephfs with Fuse instead of the kernel, the NFS client write >> > is >> > fast: >> > >> > dd if=/dev/zero of=fuse01 bs=4k count=1 >> > 1+0 records in >> > 1+0 records out >> > 4096 bytes (4.1 kB) copied, 0.026078 s, 157 kB/s >> > >> >> In this case, ceph-fuse sends an extra request (getattr request on >> directory) to MDS. The request causes MDS to flush its journal. >> Whether or not client sends the extra request depends on what >> capabilities it has. What capabilities client has, in turn, depend on >> how many clients are accessing the directory. In my test, nfs on >> ceph-fuse is not always fast. >> >> Yan, Zheng >> >> >> > Does anyone know what's going on here? >> >> >> >> > >> > Thanks >> > >> > >> > _______________________________________________ >> > ceph-users mailing list >> > ceph-users@xxxxxxxxxxxxxx >> > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >> > >> _______________________________________________ >> ceph-users mailing list >> ceph-users@xxxxxxxxxxxxxx >> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > > _______________________________________________ > ceph-users mailing list > ceph-users@xxxxxxxxxxxxxx > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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