Veeam Backup & Replication has the ability to connect directy into the storage area network which results in fast backup speeds. The Veeam Backup Server can read data direct from the VMFS volumes without going through the ESX server over the LAN.
If a VMFS volume is attached to a Windows server, make sure automount is disabled. This is done default by the installation procedure of Veeam Backup & Replication v5. If automount is set to enable, the volume will be re-signatured which will mean the ESX-hosts will not be able to access it.
Another method preventing Windows re-signature the volume is giving the Veeam backup server read only access to VMFS volumes it needs to access for backup. However not all storage types support read only modes for a specific server. For example Dell Equallogic and HP EVA do not support this.
While configuering the Veeam backup server for read only access to volumes on a HP MSA2000 I found the configuration is not straight forward. To configure a volume for read only perform the following tasks from the Storage Management Utility:
1. select the volume
2. select Provisioning
3. Select Default mapping
4. Set to not mapped
5. Select explicit mapping
6. Select each volume which needs to be accessed by ESX hosts to read/write. Do this by selecting the host, enable map and select a LUN number
7. Select the Veeam backup server, select map and set to read only.