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RE: [Xen-users] Share of disks in read only between dom0 and domU.

  • To: "Michel Gaudet" <Michel.Gaudet@xxxxxxxx>, <xen-users@xxxxxxxxxxxxxxxxxxx>
  • From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
  • Date: Thu, 27 Sep 2007 19:41:49 +1000
  • Delivery-date: Thu, 27 Sep 2007 02:42:42 -0700
  • List-id: Xen user discussion <xen-users.lists.xensource.com>
  • Thread-index: AcgA3qNoQMz3pBbQQ3Km21L0m8jz8gACwyGQ
  • Thread-topic: [Xen-users] Share of disks in read only between dom0 and domU.

> Hello !
> Because of a special config of my grub boot system, i try to export in
> domU, in read
> only mode, one of my disk partition mounted in the dom0 (in RW)  and i
> don't succeed
> because xen refuse to export this disk partition in a domU.

I think you can append a '!' do the permissions, eg 'r!' or 'w!' (or
maybe it was a '+'?) if you want to force xen to do your bidding, even
if xen thinks it's not a good idea. I've done this with OCFS2 before.

But for a non-cluster aware filesystem, you're asking for trouble. DomU
will cache filesystem data which Dom0 may write to, leaving DomU with
out of data information (nothing to tell it to re-read). If everyone
mounts the filesystem ro then you should be fine

I think you can configure Dom0 to mount the filesystem with no write
caching (eg synchronous mode), but I don't think you can tell DomU to
mount it with no read caching, and even if you could, you would surely
run into race conditions where Dom0 is changing data even as DomU is
reading it.


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