Am Donnerstag 15 März 2007 schrieb Leon Kolchinsky:
> Hello All,
>
>
> After reading http://oss.sgi.com/projects/xfs/faq.html#wcache
> and some posts on the list I've got the following question:
>
> If I have disabled write cache on the disk (hdparm -W0 /dev/hda) and by
> default FS is mounted with "barrier" enabled, Is there any taste in
> enabling "barrier"(by default) because write cache is disabled anyway
> or may be it's a good idea to mount with "nobarriers" in this case?
Hello Leon!
It is not needed to enable barriers when write cache is disabled. Enabling
barriers in this case shouldn't have any visible effect I think.
> I thought that "barrier" is on by default to somewhat minimize
> potential dangers of enabled write cache? But if write cache is
> disabled, would "barrier" option just slow down the FS performance
> (which is already slowed down by "hdparm -W0 /dev/had" anyway)?
I think it wouldn't slow down any more, except maybe a minimal slow down
due to a little bit more of code executed inside XFS.
But why do you want to disable write cache in the first case? As long as
you are using 2.6.17.7 or later you can safely enable barriers and and
write cache. At least that is my experience upto 2.6.20.1 with old IDE
drivers and now since some hours on my ThinkPad T42 2.6.20.3 with libata
drivers.
With write barriers XFS and enabled write cache, XFS will not be as fast
as without write barriers and with enabled write cache - which is the
unsafe combination -, but it will still be faster than with disabled
write cache.
Regards,
--
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
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