The quick and simple answer to this should be that everything will work fine. Most SAN vendors support the environment you describe but check with your vendor to make sure. Be aware though that if you are going to be doing SAN-based backup during production hours, your performance may be impacted when running streaming tape backup while also accessing your production data.
A third HBA helps here. Say you have the capability to "break off" a mirror (BCV) to do backup, and you are running the backup engine on the production server. When the production server begins to pull read data from the BCV as fast as it can to the tape library, your load-balanced access to production will be impacted. If you use a third HBA to the tape pool, you keep humming along (except for the CPU cycles need to run the backup job).
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This was first published in March 2002