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

[steve at linuxsuite.org]

> 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
>>
>>
>>
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