On 4/12/11 1:33 PM, Lars Wilke wrote: > Hi, > > There are quite a few threads about ZFS and performance difficulties, > but i did not find anything that really helped :) > Therefor any advice would be highly appreciated. > I started to use ZFS with 8.1R, only tuning i did was setting > > vm.kmem_size_scale="1" > vfs.zfs.arc_max="40000M" > > The machines are supermicro boards with 48 GB ECC RAM and 15k RPM SAS > drives. Local read/write performance was and is great. > But exporting via NFS was a mixed bag in 8.1R. > Generally r/w speed over NFS was ok, but large reads or writes took > ages. Most of the reads and writes were small, so i did not bother. > > Now i upgraded one machine to 8.2R and i get very good write performance > over NFS but read performance drops to a ridiciously low value, around > 1-2 MB/s. While writes are around 100MB/s. The network is a dedicated > 1GB Ethernet. The zpool uses RAIDZ1 over 7 drives, one vdev. > The filesystem has compression enabled. Turning it off made no > difference AFAICT > > Now i tried a few of the suggested tunables and my last try was this > > vfs.zfs.txg.timeout="5" > vfs.zfs.prefetch_disable="1" > vfs.zfs.txg.synctime=2 > fs.zfs.vdev.min_pending="1" > fs.zfs.vdev.max_pending="1" > > still no luck. Writting is fast, reading is not. Even with enabled > prefetching. The only thing i noticed is, that reading for example 10MB > is fast (on a freshly mounted fs) but when reading larger amounts, i.e. > couple hundred MBs, the performance drops and zpool iostat or iostat -x > show that there is not much activity on the zpool/hdds. > > It seems as if ZFS does not care that someone wants to read data, also idle > time of the reading process happily ticks up and gets higher and higher!? > When trying to access the file during this time, the process blocks and > sometimes is difficult to kill, i.e. ls -la on the file. > > I read and write with dd and before read tests i umount and mount the > NFS share again. > > dd if=/dev/zero of=/mnt/bla size=1M count=X > dd if=/mnt/bla of=/dev/null size=1M count=Y > > mount is done with this options from two centos 5 boxes: > rw,noatime,tcp,bg,intr,hard,nfsvers=3,noacl,nocto > > thanks > --lars > > _______________________________________________ > freebsd-questions@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-questions > To unsubscribe, send any mail to "freebsd-questions-unsubscr...@freebsd.org"
I refer you to this post by Jeremy Chadwick with tuning values *AND* their actual explanation. http://lists.freebsd.org/pipermail/freebsd-stable/2011-February/061642.html _______________________________________________ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "freebsd-questions-unsubscr...@freebsd.org"