There are a number of different ways that this is accomplished, and they generally have an alternate copy of the data, such as a business continuous volume (BCV) or a split-mirror, or perhaps a snapshot, and then present that data to some other system or device that can copy the data to tape. The typical way that this is done is via a dedicated backup server. So, you have a server that's being backed up. It's using data that's on the SAN, which is being controlled and split off and snapped by a backup server. Then, that extra copy of the data is presented to another server that transfers the data to tape.
There is another way, which is truly server free, which uses something called third-party copy, which is a SCSI command. Third-party copy can tell a device, such as a disk array that supports the command, to actually copy its data straight to a tape drive without having to go through a server.
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This was first published in May 2008