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

On 21 September 2012 21:30, Daniel P. Berrange <berrange(a)redhat.com&gt; wrote: > 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. > Thanks very much! That's very helpful to know. Is this something that someone has already done before (booting multiple KVM guests from shared read-only root file system) or am I on my own with this?