Looking at deploying a multi-server install of Zimbra Network edition 8.

In trying to ensure customers experience the amazing service Zimbra can provide I am looking to size mailbox stores appropriately.

Customers would have user mailboxes of 25Gb and so I would like to know if anyone knows roughly how large a disk could be before performance is degraded?

Hosted on a VMware platform with iSCSI software connections to a SAN with SAS drives.