On Jun 14, 2012, at 1:35 PM, Robert Milkowski wrote:

>> The client is using async writes, that include commits. Sync writes do
>> not need commits.
>> What happens is that the ZFS transaction group commit occurs at more-
>> or-less regular intervals, likely 5 seconds for more modern ZFS
>> systems. When the commit occurs, any data that is in the ARC but not
>> commited in a prior transaction group gets sent to the ZIL
> Are you sure? I don't think this is the case unless I misunderstood you or
> this is some recent change to Illumos.

Need to make sure we are clear here, there is time between the txg being
closed and the txg being on disk. During that period, a sync write of the
data in the closed txg is written to the ZIL.

> Whatever is being committed when zfs txg closes goes directly to pool and
> not to zil. Only sync writes will go to zil right a way (and not always, see
> logbias, etc.) and to arc to be committed later to a pool when txg closes.

In this specific case, there are separate log devices, so logbias doesn't apply.
 -- richard


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