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Thread: ZFS native slow.

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  1. #1
    Join Date
    Nov 2009
    Ubuntu 9.10 Karmic Koala

    ZFS native slow.

    I'm trying the native ZFS module on my home fileserver. So far with pretty disappointing results.
    Writing degrades quickly to 5-10 MB/s, and reading is just plain ridiculous at 300 KB/s. I need som help tuning this thing. Please?

    Some details:

    • Ubuntu 10.04.2 LTS 64bit, 8GB RAM.
    • Installed ubuntu-zfs metapackage version "3~lucid (ubuntu-zfs)" (
    • zpool: 4 x 2TB Samsung spinpoint F4 disks in a RAIDZ1:
          tank        ONLINE       0     0     0
            raidz1-0  ONLINE       0     0     0
              sda     ONLINE       0     0     0
              sdb     ONLINE       0     0     0
              sdc     ONLINE       0     0     0
              sdd     ONLINE       0     0     0

    When I start copying files into the zpool, things start out great, but then degrades quickly. When the zfs kernel module has aloocated all system memory, kswapd0 steps into action and performance of the whole system grinds to a near-halt.

    Example output of iostat of a file-copy on a freshly booted system:

    # zpool iostat 5
                   capacity     operations    bandwidth
    pool        alloc   free   read  write   read  write
    ----------  -----  -----  -----  -----  -----  -----
    tank        1,34T  5,91T  2,13K     18  1,46M  1,86M
    tank        1,34T  5,91T  3,65K    438  2,48M  51,9M
    tank        1,34T  5,91T  3,53K    635  2,39M  73,0M
    tank        1,34T  5,91T  3,34K    784  2,27M  90,6M
    tank        1,34T  5,91T  3,68K    379  2,48M  44,9M
    tank        1,34T  5,91T  3,56K    800  2,41M  94,8M
    tank        1,34T  5,91T  3,08K    412  2,09M  49,0M
    tank        1,34T  5,91T  2,75K  1,02K  1,86M  81,0M
    tank        1,34T  5,91T  2,47K  13,8K  1,66M  24,5M
    tank        1,34T  5,91T  1,65K  61,4K  1,12M  35,5M
    tank        1,34T  5,91T  2,73K  50,1K  1,85M  29,1M
    tank        1,34T  5,91T  2,67K  34,8K  1,81M  20,4M
    tank        1,34T  5,91T  2,80K  50,0K  1,90M  29,1M
    tank        1,34T  5,91T  2,62K  31,8K  1,78M  18,7M
    tank        1,34T  5,91T  2,27K  18,3K  1,55M  10,9M
    tank        1,34T  5,91T  2,51K  16,4K  1,70M  9,59M
    I would expect write performance to be 50+ MB/s or something.

    I tried to limit the memory consumption by setting the zfs_arc_max to (5GB, right?) with this:

    # echo "5000000000" > /sys/module/zfs/parameters/zfs_arc_max
    That doesn't seem to do anything. After rebooting it is reset to zero. So I guess I'm not doing this right? How do I tell ZFS to limit memory usage? And how do I make it stick?

    Also, somewhere it was suggested to disable primarycache:

    # zfs set primarycache=none tank
    That seems to make kswapd0 slightly less active. General performance is pretty much the same...

    Please help
    Last edited by bomix; March 5th, 2011 at 04:38 AM. Reason: Corrected /sys/module/... path

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