Re: xbd0: WARNING: cache flush not supported by backend

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Fri, Sep 24, 2010 at 05:55:43PM +0200, Pierre-Philipp Braun wrote:
> 
> Hi,
> 
> network worked (once) with patched domU installer
> (http://blog.yellowback.net/uploads/netbsd-5.99.27-xenfront-rx-copy.patch)
> but there seem to be another little issue with -current domU.  After the
> netbsd partitions get formatted I get,
> 
>      Status: Finished
>     Command: /sbin/mount -tffs -o log /dev/xbd0a /targetroot/
>      Hit enter to continue
> --------------------------------------------------------------------------------
> xbd0: WARNING: cache flush not supported by backend

I guess this is because you're using -o log on the filesystems ?
In order to work reliably, NetBSD needs to be able to flush the underlying's
disk cache. This needs support in the backed driver, but this was not
provisionned by the Xen peoples (I'm not sure how or if linux manages
to run reliably a journaled filesystem without it) so it's a NetBSD
extention to the Xen block device protocol.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--