# [OmniOS-discuss] Pliant/Sandisk SSD ZIL

Derek Yarnell derek at umiacs.umd.edu
Mon Feb 17 22:48:58 UTC 2014

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    Hi,

    So we bought a new Dell R720xd with 2 Dell SLC SSDs which were shipped
    as a Pliant-LB206S-D323-186.31GB via format.  The bulk of the storage is
    just a 6+2 RaidZ2 with 3TB disks.  When doing a simple untar (40MB/2000
    files) over NFS (synchronous IO) having the mirrored slog of Pliant SSDs
    seems to offer horrendous performance.  On the order of 18-20 OPs per
    second (via zpool iostat -v 1).  We have a number of other ZFS builds
    with ZeusRAM slogs and they work very well and while the Pliant may not
    be as good a choice it shouldn't be as bad as this.

    # zfs get sync,dedup,logbias,compression,checksum zpool0
    NAME    PROPERTY     VALUE          SOURCE
    zpool0  sync         standard       default
    zpool0  dedup        off            default
    zpool0  logbias      latency        default
    zpool0  compression  off            default
    zpool0  checksum     on             default

    Adding a ramdisk slog device makes everything perform as expected.
    Setting sync=disabled of course makes things all better.

    # zpool status zpool0
      pool: zpool0
     state: ONLINE
      scan: none requested
    config:

            NAME                       STATE     READ WRITE CKSUM
            zpool0                     ONLINE       0     0     0
              raidz2-0                 ONLINE       0     0     0
                c1t5000C50057EC4B73d0  ONLINE       0     0     0
                c1t5000C50057EC6EABd0  ONLINE       0     0     0
                c1t5000C50057EC7CB7d0  ONLINE       0     0     0
                c1t5000C50057EC8F23d0  ONLINE       0     0     0
                c1t5000C50057EC998Bd0  ONLINE       0     0     0
                c1t5000C50057ECB1BBd0  ONLINE       0     0     0
                c1t5000C50057ECFEE7d0  ONLINE       0     0     0
                c1t5000C50057ED03F7d0  ONLINE       0     0     0
            logs
              mirror-1                 ONLINE       0     0     0
                c3t5001E820026DA2CAd0  ONLINE       0     0     0
                c3t5001E820026DA45Ad0  ONLINE       0     0     0

    errors: No known data errors

    --
    Derek T. Yarnell
    University of Maryland
    Institute for Advanced Computer Studies

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