[libvirt-users] sharing read-only LOCAL disks among KVM guests

[Daniel P. Berrange]

On Fri, Sep 21, 2012 at 09:22:24PM +1000, Amos Shapira wrote:
> Hello,
> 
> Is it possible to share a single host's Logical Volume among multiple local
> KVM guests which mount it read-only?
> 
> I'm asking this because I have an idea to run multiple idential KVM guests
> (they all have exactly the same software installed on them), booting them
> from a shared local Logical Volume read-only root file system, or
> alternatively let them share the bulk of the software (/usr, /opt, /lib)
> from a common KVM host Logical volume.
> 
> Is this possible? All my searches so far failed to turn up anything like
> this.

>From the libvirt POV, there's nothing much todo except add <readonly/>
inside the <disk> element. This will ensure QEMU only gets given read
permission on the disk backend. The important thing is to then make sure
your guests actually mount the filesystem with the readonly flag.

> Would it be possible using qcow2 instead of raw LV? If so - would it be
> worth the performance hit of switching from LV to qcow2?

The type of backend storage doesn't really affect things if the
disk is fully readonly.

Daniel
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