I'd like to know your experience of using Zimbra in production systems (not for testing or demo) on Virtual Machines, expecially on VMware Virtual Infrastructure 3 (ESX and ESXi), KVM and Xen.
Please report if possibile dome details about the Virtual infrastructure you are using, the Zimbra configuration (single server or multi server) and how many users in the system.
We are testing Zimbra 5.0.16 OSE in Single Server on ESX 3.5 for about 50 users, with Ubuntu 8.04 64 bit, 2vCPU and 3GB of RAM assigned and reserved to the VM, about 100GB of /opt/zimbra for mailbox data on a local VMFS partition on RAID5, and it seems to behave well (we are in pre-production phase).
We know that Zimbra is heavily based on Java and that Java currently suffers a bit in a virtualized environment compared to native; on the other side it seems that the gap is going to disappear in the near future (see for example  )
Awaiting your feedback.
: VMware: VROOM!: ESX Runs Java Virtual Machines with Near-Native Performance