We have a Dell Equal Logic and QNAP NAS. Our Zimbra is running from Dell Equal Logic with plenty of spare storage remains. We have been arguing which will be the ideal setup for Zimbra backup:

1. Zimbra Backup on Dell Equal Logic:
By placing our backup on our premiere storage (since it has plenty of storage available at the moment anyway), we can enjoy the additional reliability and performance of this SAN storage for Zimbra Backup.

2. Zimbra Backup on QNAP NAS:
By placing our backup on separate storage, there is additional safety whereby if one storage crash or unavailable, we have at least another set to recover from (despite QNAP is of lower reliability and performance which may extend backup time). If we decide on this route, we need to decide to mount QNAP NAS directly to Zimbra VM as NFS, or indirectly to Zimbra VM thru iSCSI as VMFS.

2a. Zimbra Backup on QNAP NAS as VMFS:
QNAP NAS iSCSI is certified by vmware and we have been able to mount a iSCSI volume into ESX as a VMFS datastore. The only disadvantage is that it does not have a security to set which servers to share or not to share to. Thus, anyone can access to QNAP once the iSCSI volume is created. (It does has a iSCSI Advanced ACL to handle this problem.)

2b. Zimbra Backup on QNAP NAS as NFS:
With NFS, we will be able to access to Zimbra Backup directly on the QNAP without going thru the ESX host. But I believe some vSphere features available on the VMFS will not be available on the NFS right?