Re: [Xen-users] Xen domU filesystem best-practices question

[Tom Brown <xensource.com@xxxxxxxxxxxxxxxxxxx>]

On Wed, 25 Jul 2007, Nico Kadel-Garcia wrote:

> Jeff Bachtel wrote:
> >  For file-backed disk images used for domUs, what is the current
> >  best-practice filesystem to use? That is, the filesystem with the
> >  fewest edge cases and failure modes.
> >
> >  I was told (6 months back or so), to absolutely not use a journalled
> >  filesystem on a file-backed image, and so I started moving to ext2. Is
> >  this advice still pertinent, or would a journalled filesystem now be
> >  better (XFS or ext3, for instance).
> >
> >  Thanks,
> >
> >  Jeff
> I've been using ext3 with little trouble. Ext3 has the advantage of coping, 
> successfully, with 50,000 files in one directory without hiccup-ing, which 
> ext2 always had trouble with.
I would assume the original suggestion was due to the journalling 
filesystem's requirement that the journal is written before the raw data. 
With a file-backed image I can imagine that the write ordering is at the 
discretion/mercy of the dom0 filesystem layer... whereas with a virtual 
block device it should be "as requested" by the domU. Could you give your 
domU's a small block device to use for the journal(s)?
That said, I would expect the modern ext2 logic can handle all the ext3 
options like dir_index (which should help with big directories) as long as 
they aren't journal related.
All the above said, I'm not a developer, just an old sys-admin who likes 
to pretend he understands how things work :)
-Tom

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