Ask the Expert

Keeping data within the SAN

I'm evaluating SAN solutions for my shop. Compaq tells me they have a SAN solution (the MA8800) that includes an integrated tape drive for backup purposes. My contact says the backup data would not leave the SAN, come to the server, and go back to the SANs tape drive when backing up the data. This would be phenomenal since the data would never reach the CPU, it would stay inside the SAN when performing a backup.

My OS is HPUX 11.0. As far as I know, if I use a backup program on my HPUX box the data will traverse the SAN, come into the CPU and go back to the tape drive. Is this correct? Am I missing something?

When I asked my HP salesman about a tape drive in the SAN he says the best he could think of is including an FC tape drive as another device attached to the SAN switch. Would this work? Would the data stay inside the SAN? Would it make the round trip to the CPU?

Regards,


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The typical way to design a SAN backup system is to dedicate master and media servers for the backup. It is true that only an agent on the application server will be used to determine what data has changed on the application server or handle locking for file systems.

The master server handles a database that keeps track of all backup activity for the system. The media servers are used to actually move the data from the disk through the switch to the tape system. If you use this approach, you can scale your SAN by adding disk, switches, media servers, and tape drives as appropriate. The nice thing is that the application servers are left to what they were meant to do: Run applications.

Most FC tape drives today are FC-LP (Loop) and will use an FL port from your switch. So, if you define the SAN to include the backup servers (which you should - since the SAN is more than just switching hardware), then you are correct: The data will stay inside the SAN, using the media servers for data movement.

Jim

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This was first published in September 2001

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