[OmniOS-discuss] Pliant/Sandisk SSD ZIL

[Derek Yarnell]

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