# [OmniOS-discuss] No I/O on ZIL logs?

steve at linuxsuite.org steve at linuxsuite.org
Mon Jan 7 12:08:58 EST 2013

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    > Steve,
    > The ZIL is only used for synchronous I/O.  Normally, ZFS writes are
    > async to the application.  That is, they are buffered in memory and
    > flushed out periodically to stable storage.  If an application opens a
    > file with one of the sync flags (O_SYNC, O_DSYNC, etc.) or calls
    > fsync(2), then you will see traffic to a slog device.

            Aha!! this seems to do the trick..

           zfs set sync=always data1

          default is sync=standard

          Lots of ZIL I/O now.

         thanx - steve

    >
    > Eric
    >
    > On Mon, Jan 7, 2013 at 10:58 AM,  <steve at linuxsuite.org> wrote:
    >> Howdy!
    >>
    >>        I am doing some testing of zfs on OmniOS. It seems that the ZIL
    >> logs
    >> never get any I/O.  I have a zpool as follows
    >>
    >> root at live-dfs-1:~# zpool status data1
    >>   pool: data1
    >>  state: ONLINE
    >>   scan: resilvered 937G in 17h53m with 0 errors on Sat Jan  5 08:52:32
    >> 2013
    >> config:
    >>
    >>         NAME                         STATE     READ WRITE CKSUM
    >>         data1                        ONLINE       0     0     0
    >>           raidz2-0                   ONLINE       0     0     0
    >>             c5t5000C500525BFB31d0s0  ONLINE       0     0     0
    >>             c5t5000C500525C2F91d0s0  ONLINE       0     0     0
    >>             c5t5000C500525C72B1d0s0  ONLINE       0     0     0
    >>             c5t5000C500525C9673d0s0  ONLINE       0     0     0
    >>             c5t5000C500489956C1d0s0  ONLINE       0     0     0
    >>             c5t5000C500525EB2B9d0s0  ONLINE       0     0     0
    >>             c5t5000C500525F2297d0s0  ONLINE       0     0     0
    >>             c5t5000C50045561CEAd0s0  ONLINE       0     0     0
    >>             c5t5000C50048990BE6d0s0  ONLINE       0     0     0
    >>             c5t5000C500489947A8d0s0  ONLINE       0     0     0
    >>         logs
    >>           mirror-1                   ONLINE       0     0     0
    >>             c1t2d0                   ONLINE       0     0     0
    >>             c1t4d0                   ONLINE       0     0     0
    >>         cache
    >>           c1t5d0                     ONLINE       0     0     0
    >>
    >> errors: No known data errors
    >>
    >>       Then I simply have a script that does some writing to the zpool.
    >>
    >>      If I run
    >>
    >>     zpool iostat -v data1 5
    >>
    >>    I get output like this ( see below). Why is there never any I/O to
    >> the
    >>  logs? I understood that these logs would be written first before
    >>  the data is commited to the zpool. I can't find any evidence that this
    >> is
    >> happening. Lights on hardware don't blink either to indicate activity. I
    >> have verified that the disks used for the ZIL are writable.
    >>  Why is this not happening? How can I make it so?
    >>
    >>       thanx - steve
    >>
    >>  root at live-dfs-1:~# zpool iostat -v data1 5
    >>
    >>                                 capacity     operations    bandwidth
    >> pool                         alloc   free   read  write   read  write
    >> ---------------------------  -----  -----  -----  -----  -----  -----
    >> data1                        9.98T  16.8T      0  3.14K      0   113M
    >>   raidz2                     9.98T  16.8T      0  3.14K      0   113M
    >>     c5t5000C500525BFB31d0s0      -      -      0    146      0  16.6M
    >>     c5t5000C500525C2F91d0s0      -      -      0    147      0  16.6M
    >>     c5t5000C500525C72B1d0s0      -      -      0    146      0  16.6M
    >>     c5t5000C500525C9673d0s0      -      -      0    147      0  16.6M
    >>     c5t5000C500489956C1d0s0      -      -      0    146      0  16.6M
    >>     c5t5000C500525EB2B9d0s0      -      -      0    146      0  16.6M
    >>     c5t5000C500525F2297d0s0      -      -      0    146      0  16.6M
    >>     c5t5000C50045561CEAd0s0      -      -      0    146      0  16.6M
    >>     c5t5000C50048990BE6d0s0      -      -      0    146      0  16.6M
    >>     c5t5000C500489947A8d0s0      -      -      0    146      0  16.6M
    >> logs                             -      -      -      -      -      -
    >>   mirror                         0   148G      0      0      0      0
    >>     c1t2d0                       -      -      0      0      0      0
    >>     c1t4d0                       -      -      0      0      0      0
    >> cache                            -      -      -      -      -      -
    >>   c1t5d0                      111G  7.51M      0    179      0  18.6M
    >> ---------------------------  -----  -----  -----  -----  -----  -----
    >>
    >>
    >>                                 capacity     operations    bandwidth
    >> pool                         alloc   free   read  write   read  write
    >> ---------------------------  -----  -----  -----  -----  -----  -----
    >> data1                        9.99T  16.8T      1  3.56K  10.3K   105M
    >>   raidz2                     9.99T  16.8T      1  3.56K  10.3K   105M
    >>     c5t5000C500525BFB31d0s0      -      -      0    158  1.58K  15.9M
    >>     c5t5000C500525C2F91d0s0      -      -      0    168  2.38K  15.9M
    >>     c5t5000C500525C72B1d0s0      -      -      0    163  2.38K  15.9M
    >>     c5t5000C500525C9673d0s0      -      -      0    154    810  15.9M
    >>     c5t5000C500489956C1d0s0      -      -      0    163  1.58K  15.9M
    >>     c5t5000C500525EB2B9d0s0      -      -      0    161  1.58K  15.9M
    >>     c5t5000C500525F2297d0s0      -      -      0    158      0  15.9M
    >>     c5t5000C50045561CEAd0s0      -      -      0    165      0  15.9M
    >>     c5t5000C50048990BE6d0s0      -      -      0    149      0  15.9M
    >>     c5t5000C500489947A8d0s0      -      -      0    153      0  15.9M
    >> logs                             -      -      -      -      -      -
    >>   mirror                         0   148G      0      0      0      0
    >>     c1t2d0                       -      -      0      0      0      0
    >>     c1t4d0                       -      -      0      0      0      0
    >> cache                            -      -      -      -      -      -
    >>   c1t5d0                      111G     8M      1    260  1.38K  26.0M
    >>
    >>
    >>
    >> _______________________________________________
    >> OmniOS-discuss mailing list
    >> OmniOS-discuss at lists.omniti.com
    >> http://lists.omniti.com/mailman/listinfo/omnios-discuss
    >

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