When clients have high availability requirements for their Plone site, we recommend using the RelStorage implementation for the ZODB, combined with the PostgreSQL database platform. This post describes how to combine ZFS replication with PostgreSQL.
Six Feet Up has been heavily involved in a major hosting infrastructure upgrade that includes moving machines between racks...
It appears that, if you use some of the more advanced networking technologies built into FreeBSD, it is possible to put yourself into a bit of a pickle...