# [OmniOS-discuss] zpool/zfs settings optimization

Paul B. Henson henson at acm.org
Wed May 29 19:11:28 EDT 2013

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    I'm getting down to the wire on the home storage server I've been
    working on building for altogether too long. Right now I'm trying to
    finalize the zpool/zfs settings I'm going to create the rpool and bulk
    storage pool with.

    The rpool is going to be a mirror of the first partitions of two 256G
    SSDs (I haven't decided how big to make that, it looks like a default
    install of omnios takes up less than 1G, and I don't anticipate
    installing that much more at the OS level).

    The storage pool is going to made up of 2 x 6 RAIDZ2 WD Red 3TB drives,
    with a partition of an Intel DC 3700 as log, and the remaining two
    partitions of the rpool SSDs as l2arc.

    There's going to be a wide variety of stuff stored on the storage pool,
    from mp3/flac/aac music, to DVD/bluray rips, and basic home directory
    stuff like documents and pictures. A big chunk will be dedicated to my
    mythtv system and contain OTA ATSC mpeg2 transport streams.

    For the rpool I plan to enable lz4 compression for the entire pool. For
    the storage pool I will probably disable it for filesystems containing
    mostly noncompressible stuff and enable it for home directory like
    filesystems containing documents and other things more likely to be
    compressible. I think I'm going to set atime=off globally on both pools,
    I can't think of any reason that data would be worth the extra write load.

    While I'm going to leave it the default for rpool, I'm thinking I'm
    going to set failmode=continue on the storage pool.

    If I understood correctly, there's really no value in changing the
    default recordsize unless you're using an application like a database
    that you know always reads in chunk sizes smaller and reading in the
    entire record would be a waste. I thought I remembered reading somewhere
    that one of the zfs forks had increased the maximum recordsize to
    something bigger, like 2M or 10M or something, but I can't seem to find
    a reference to it now. For filesystems which store only large files (OTA
    HD recordings are generally multi-gigabyte) it seems that would be more
    efficient. Is anybody looking at increasing the maximum record size in
    illumos zfs?

    While I understand what the primarycache and secondarycache attributes
    control, I'm not really clear on when it might be desirable to change
    them. Are there any routine scenarios where you might want to configure
    them other than the default, or is that just limited to specific
    deployments such as databases where you want to avoid double buffering
    of data in memory?

    I was planning on making the storage available to my mythv server over
    NFS. I was thinking about setting logbias=throughput for that file
    system, as intuitively that would seem a better tuning for multiple
    streams being written at once. Or, I could possibly set sync=disabled on
    that file system to completely avoid the overhead of NFS synchronous
    writes. If there's a failure during a recording and I lose five minutes
    of the end, oh well…

    Moving on to kernel tunables, I was thinking of enabling l2arc
    prefetching (l2arc_noprefetch=0). I'm also thinking of increasing
    l2arc_write_max to better avail of more modern SSDs, but I'm not sure to
    what. At some point will the default zfs kernel tunables be updated to
    match currently available devices rather than the more limited flash
    devices of yesteryear?

    Any thoughts on these mentioned settings/tunables, or recommendations of
    other things I might want to do?

    Thanks much…

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