Re: [Xen-users] modifying file-systems in Dom0 while mounted read-only in DomU

[Luciano Miguel Ferreira Rocha <strange@xxxxxxxxxxxxx>]

On Tue, Mar 27, 2007 at 02:54:46PM +0200, Reinhard Brandstädter wrote:
> So while it's not possible to create DomUs with disks that are currently 
> mounted in the Dom0, it is possible to mount disks in the Dom0 that are 
> currently in use by a DomU?

That's essentially the same thing.

> Although this is a nice feature  - in my case these two DomUs are forming a 
> cluster and the common configuration resides on the read-only disk - it seems 
> dangerous to me.
> 
> Although with this feature I could seamless change the configuration of the 
> cluster :-) :
> - mount the partitition in Dom0
> - restart one DomU and let it gain the service with changed configuration
> - restart the second DomU with the new configuration

You should be able to see new data without rebooting by droping cache:
echo 3 > /proc/sys/vm/drop_caches

But I suggest using a cluster filesystem instead (OCFS2, GFS, etc.). Then
the changes will be visible everywhere you mount the filesystem.

IIRC, you'll have to specify the virtual disk to xen with '...,w!' to
allow multiple mounting of the same partition in read/write mode.

-- 
lfr
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