RE: [Xen-users] unionfs with xen

[Simon Hobson <linux@xxxxxxxxxxxxxxxx>]

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
>
> kindly guide me..
I don't know - not something I've ever worked with.

A quick look in the Xen manual 
(http://tx.downloads.xensource.com/downloads/docs/user/) comes up 
with this :
> Block devices should typically only be shared between domains in a 
> read-only fashion otherwise the Linux kernel's file systems will get 
> very confused as the file system structure may change underneath 
> them (having the same ext3 partition mounted rw twice is a sure fire 
> way to cause irreparable damage)! Xend will attempt to prevent you 
> from doing this by checking that the device is not mounted 
> read-write in domain 0, and hasn't already been exported read-write 
> to another domain.
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.

Looking at the live CD systems (like Knoppix) might give you some ideas.

--
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
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