would async mount improve IO speed?

Bill Moran wmoran at potentialtech.com
Tue Oct 5 07:47:44 PDT 2004

Rae <z49x2vmq at gmail.com> wrote:

> File systems used to be mounted with soft-updates(?) option.
> I disable it with "tunefs -n disable ....." and mount all file system
> with "async" option but I can feel any difference.
> some said it's dangerous. Does it matter even if I'm not running any
> heavy load server?

Async greatly increases the possiblity that a hard crash (i.e. power
outage) will corrupt the disk such that it will be impossible to
repair the filesystem, or that data will be corrupted or lost.  If
you have perfect power, and you can be 100% sure that your system will
never hard boot, then there is no danger in async.

Softupdates has 90% of the performance of async, with 90% of the
safety of sync.  This is why you won't see a big performance 
improvement unless you specifically test for it.

Since softupdates is so fast, I can see only a few edge cases where
it makes sense to use async.

Bill Moran
Potential Technologies

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