I have Zimbra ZCS 6.0.12 on ubuntu 08.04 64 bit. I need to fix upgrade to the current version of Zimbra ZCS (version 8) with the current version of ubuntu (12.04 64 bit version) with minimum downtime. I have about 5,000 email accounts. The system consists of 1x mailbox server, 1x ldap master, 1x ldap replica, 3x gateway.
How will this solve most preferably?
Thank you for all the answers.