Backups of XserveRAID data to a SAN attached drive/library will fail if the connection between the host and the RAID unit and the connection between the host and the drive/library are not physically or logically separated.
When attempting to run a File System backup of data located on an XserveRAID volume, to a tape drive located in the same SAN without physical or logical separation of the paths to host, the backup will fail. The tape used for the backup is then marked as Read Only. Backups of local data to the tape drive are successful. Likewise backups of XserveRAID data to a VTL created on local disk are successful.
Connections must be logically or physically separated to ensure a consistent communication path. The attached document details various solution options according to hardware setup. This document communicates the results of an interoperability test between NetVault, Apple, Qlogic FC switch, and Exabyte tape. The theory remains the same irrespective of which switch or tape drive/library is used.
BakBone SFDC Solution Number: 00001249