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Re: [Xen-users] unionfs with xen


  • To: Xen-users@xxxxxxxxxxxxxxxxxxx
  • From: "Fajar A. Nugraha" <fajar@xxxxxxxxx>
  • Date: Fri, 17 Apr 2009 20:46:28 +0700
  • Cc:
  • Delivery-date: Fri, 17 Apr 2009 06:47:13 -0700
  • List-id: Xen user discussion <xen-users.lists.xensource.com>

> Pallab Chakrabarty wrote:
>
>>> Are you trying to have a common filesystem image
>>> shared by many DomUs, and use unionfs to allow
>>> each DomU to have it's own modified version ?
>
>> YES
>>

> Now, if you are prepared to do the unionfs stuff in the DomU then I'd guess
> you could export the shared block device read-only to each guest, plus a
> separate read-write volume per guest to union with it.

You didn't mention what your primary goal is.
If your goal is to save space, then IMHO it's not worthed.

One, as Simon mentioned, you need to do union in domU. That means
modifying domU. Too much effort for a general purpose domU. Unless of
course if your goal is to create something like Live CD where unionfs
features is essentional, and performance doesn't really matter.

Two, an easier approach (as in you don't need to have a special domU)
to save space would be to use tap:qcow, LVM snapshot, or zfs-backed
zvol. All three has their own advantage and limitations. If your goal
is testing purposes for Linux PV domUs, qcow would be easiest.

Regards,

Fajar

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