We have a 20 node setup on 5.0.6 FOSS that we need to migrate to NE 5.0.9.
Are setup includes:
 LDAP Servers with 1 virtual IP (managed by heartbeat) - this virtual is what is the registered ldap url (ie: zldap.example.org). The 2nd LDAP server is basically a replica that can be converted to master with heartbeat scripts.
 Mail store servers with 1 virtual IP and connected SAN (maintained by heartbeat) - this virtual IP is also the registered server name (ie: zwebmail.example.org). The 2nd mailstore is offline and used in case of hardware emergency from the primary.
 MTA Relay Servers each having their own Zimbra server identity, and a virtual IP for DNS names to point to (ie: zsmtp.example.org)
 MTA MX Servers each registered in Zimbra as zMX[01-14].example.org)
The Mail Store Primary, MTA Relays, and MTA MX Servers, all use a local LDAP Replica.
Our Goal (Simply Put) is to run 5.0.9 NE.
I see two different paths we could take
Upgrade 5.0.6 FOSS to 5.0.6 NE, then upgrade 5.0.6 NE to 5.0.9 NE
Upgrade 5.0.6 FOSS to 5.0.9 FOSS, then Upgrade to 5.0.9 NE
The sequence of upgrades is basically DB(LDAP), Mail-Store, MTA's