On 02/04/2010 09:00, Roch wrote:
> sync=disabled
> Synchronous requests are disabled. File system transactions
> only commit to stable storage on the next DMU transaction group
> commit which can be many seconds. This option will give the
> highest performance. However, it is very dangerous as ZFS
> would be ignoring the synchronous transaction demands of
> applications such as databases or NFS. Administrators should
> only use this when these risks are understood.
>
> The property can be set when the dataset is created, or dynamically,
> and will take effect immediately. To change the property, an
> administrator can use the standard 'zfs' command. For example:
>
> # zfs create -o sync=disabled whirlpool/milek
> # zfs set sync=always whirlpool/perrin
>
> The current value of 'sync' can be retrieved in the usual manner
> with 'zfs get sync' or 'zfs list -o sync'. The sync property is not
> inherited from parent datasets.
>
> 6. Resources and Schedule
> 6.4. Steering Committee requested information
> 6.4.1. Consolidation C-team Name:
> ON
> 6.5. ARC review type: FastTrack
> 6.6. ARC Exposure: open
>
A zvol can accept DKIOCSETWCE which has similar effect and
counter effect. We should be specifiying what the
interactions will be.
if sync=default
wce is obeyed
else
wce is not obeyed
however the moment a sync is set back to the default value for a given
zvol the WCE kicks in.
Is DKIOSETWCE documented somewhere?
I guess that the non default dataset sync flag will render
DKIOCSETWCE a noop.
yes,
Will the sync flag impact the return value of a DKIOCGETWCE ?
No, it won't. GETWCE will return the current WCE setting regardless of
the sync value. SETWCE will also set its value regardless of the sync
value. From API point of view manipulating WCE and sync properties are
orthogonal.
--
Robert Milkowski
http://milek.blogspot.com
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