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Rich Castagna, Editorial Director
Hmmm, that depends on what you want the backup solution to do. The backup server can only see the LUNS in the SAN that you let it see. In order for it to back up data for the other servers in your SAN, you will need to provide access to the application server LUNS to the backup server.
If your storage subsystem supports clones or snapshots, you can do this by taking a snapshot of the application servers LUNs and grant access for the backup server to the snapshot copies. You will normally have to bring down the application for a few seconds in order to create the snap unless the array supports hot snapshot copies.
I may have to ask the Web admin for this site to allow me to include diagrams in my answers since it would be sooooo much easier for you to visualize the solution from a picture rather than words. Oh well.
Since your backup server has no IP access to the application servers, you cannot use client agents on the applications servers to pass backup metadata information. This means solutions like LAN-free backup and serverless backup will have to be done manually by you. Normally under LAN-free backup, the other servers also have access to a shared tape resource and they can back up their own LUNs with the backup server acting as the traffic cop for access to the tape drives.
Server-free backup also uses IP for passing metadata between application servers and backup servers. In your case, you can attach the tape drive directly to the backup server and manually grant LUN access to that server for the application server LUNS. Make sure you don't leave that access enabled after backup is done and best case is to use snapshots or clones of your data. NT likes to write signatures on new LUNS and you may end up screwing up your production drives if not very careful.
If you use clustering, and the backup server also happens to be a cluster member that can handle resources it will already know about the LUNS. You can then fail over the resource to the backup server, and back up the data while it "owns" the LUNS.
Chris
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This was first published in August 2003