From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
To: Mark Williamson <maw48@hermes.cam.ac.uk>
Cc: xen-devel@lists.sf.net
Subject: Re: double or triple access to ext2, ext3 or other partitions
Date: Tue, 23 Nov 2004 21:06:36 +0000 [thread overview]
Message-ID: <20041123210636.GC5146@lkcl.net> (raw)
In-Reply-To: <Pine.LNX.4.60.0411231724580.3258@hermes-1.csi.cam.ac.uk>
On Tue, Nov 23, 2004 at 05:30:04PM +0000, Mark Williamson wrote:
> >2) at every point in the ext2 and ext3 filesystem drivers where
> >SMP-driven locking is performed, add in xen-semaphore usage and locking
> >(as well / instead).
>
> It's not quite that simple: the ext driver in each domain will be caching
> data related to its filesystem changes in memory. In an SMP system, both
> CPUs can see this cached data in memory, whereas separate virtual machines
> cannot see what each other are caching.
oh drat.
> Mounting the same partition is already possible using a cluster filesystem
> (like GFS). Cluster filesystems handle the extra locking correctly
> because they're designed for use with multiple hosts sharing a disk (e.g.
> over a SAN). They'll even work with multiple writers.
oooooo :)
> It is also possible to export any filesystem via NFS and have it mounted
> by multiple domains or to have copy-on-write semantics (e.g. using LVM) so
> that domains never see each others changes (thus circumventing the
> problem).
in that case, the NFS server becomes the single point of failure should
it become attacked / compromised.
thank you for your advice about gfs, i will most definitely investigate
it.
ta,
l.
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next prev parent reply other threads:[~2004-11-23 21:06 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-11-23 17:13 double or triple access to ext2, ext3 or other partitions Luke Kenneth Casson Leighton
2004-11-23 17:30 ` Mark Williamson
2004-11-23 21:06 ` Luke Kenneth Casson Leighton [this message]
2004-11-23 20:14 ` Rik van Riel
2004-11-23 21:08 ` Luke Kenneth Casson Leighton
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