For sure an All-In-One installation lets you configure a local storage
domain:
http://www.ovirt.org/Feature/AllInOne
I have one setup like this where I definied more local storage domains (aka
more mount points pointing to different disks with different speeds...)
I don't know if this can match your needs
I don't remember if you can configure local storage domain for a
non-allinone setup.
If not, I think it would be interesting to offer it as an enahncement for
future releases.
A possible workflow could be:
offer chance to add local storage only if the cluster is composed by only
one node and in that case show a big warning that adding a local storage
would prevent adding other nodes to this cluster therafter.
If trying then to add another node, show a message that it is not possible
as it has a local storage domain attached
Gianluca