Re: XFS and write barriers.

[Martin Steigerwald <Martin@lichtvoll.de>]

[-- Attachment #1: Type: text/plain, Size: 1524 bytes --]

Am Donnerstag 29 März 2007 schrieb David Chinner:
> On Thu, Mar 29, 2007 at 04:56:21PM +0200, Martin Steigerwald wrote:
> > Am Montag 26 März 2007 schrieb David Chinner:
> > > > Is there some mount flag to say "cope without barriers" or
> > > > "require barriers" ??
> > >
> > > XFs has "-o nobarrier" to say don't use barriers, and this is
> > > *not* the default. If barriers don't work, we drop back to "-o
> > > nobarrier" after leaving a loud warning inthe log....
> >
> > Hello David!
> >
> > Just a thought, maybe it shouldn't do that automatically, but require
> > the sysadmin to explicitely state "-o nobarrier" in that case.
>
> And prevent most existing XFS filesystems from mounting after
> a kernel upgrade? Think about the problems that might cause
> with XFs root filesystems on hardware/software that doesn't
> support barriers....

Hello David!

Granted. So it might turn out to be a decision between does not boot or is 
not totally safe in power outages or crashes. I see no easy default 
answer to that.

So while probably being a layering violation at least trying to disable 
the write cache on devices without cache flush support unless "-o 
nobarrier" (as in "I know what I am doing") is given, might help safety. 
But this adds complexity and a possible source for bugs. And maybe trying 
to disable write cache isn't safe on all setups?

Regards,
-- 
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA  B82F 991B EAAC A599 84C7

[-- Attachment #2: Type: application/pgp-signature, Size: 189 bytes --]