would async mount improve IO speed?

Erik Trulsson ertr1013 at student.uu.se
Tue Oct 5 07:44:17 PDT 2004

On Tue, Oct 05, 2004 at 10:34:15AM -0400, Rae 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 (as well as soft-updates) only improve performance when writing
to the disk.  Reading from the file system will not be affected by
either. "async" can be dangerous, yes.  If the computer crashes, or is
otherwise not properly shutdown, then you risk losing a *lot* of data
from an async filesystem, as well as risking leaving the filesystem
in an inconsistent state.

"async" should only be used for filesystems where both the following
holds true:

1) The system makes a lot of writes to the filesystem. (Otherwise there
   is very little performance gain to be obtained from "async".) 
2) Losing all the data on the filesystem is not a big problem. 

<Insert your favourite quote here.>
Erik Trulsson
ertr1013 at student.uu.se

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