Cyrus v2.2 and v2.3 interoperability

[Eli Ben-Shoshan]

We here at the University of Florida are running a good sized cyrus murder
setup. We have 10 cyrus v.2.2.12 backends with 9 cyrus v2.2.12 frontends and a
dedicated mupdate master running v2.2.12.

We are now in the planning phase of moving to the cyrus v2.3 branch. We will be
installing all v.2.3.7 nodes since that is what is the latest available in RHEL 5.3.

We would like to upgrade just the frontends and mupdate first since we are
redesigning our backend's storage infrastructure. Later on we plan on upgrading
the backends to v2.3 with replication.

Can this be done?
Is it safe to run v2.3 frontends and mupdate while keeping v.2.2 backends?
Should we leave mupdate at v2.2 and upgrade just the frontends to v2.3?
Are there specific versions of cyrus to avoid in this situation?
Has anyone actually done this before?

Any insights are welcomed. Thanks in advance.

-- 
Eli Ben-Shoshan