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

[Amos Shapira]

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.

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 motivation for this is two-fold:
1. Speed-up - I suspect that sharing the same disk block among all KVM
agents (we currently have 14 KVM guests on each server) should lead to
better cache utilisation and reduce disk access. Also the cost of
maintaining the mutiple identical servers and keeping them up to date could
be eating into our server's resource usage.
2. Maintenance - if I get to share the common disk image among all of them
then I only need to install/update it once instead of once for each KVM
guest (we already use Puppet but it doesn't mean it comes for free).

Thanks,

--Amos
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