Third party copy is a backup technique where an intelligent device, and not the backup server, or the server whose data is being backed up (hence third party) moves the backup data stream from disk to tape. That "intelligent device" used to always be the data router (SCSI to Fibre Channel bridge) that connected the SCSI DLT drives to the SAN fabric.
The data router used the "SCSI-3 extended copy modifications and extensions for backup and data movement support" command set which is also known as "E-Copy", "X-Copy" or "Extended Copy" commands for the SCSI-3 protocol. Over the past year or so, the E-Copy command set has been incorporated into other devices like the HDS storage arrays and Exabyte tape drives so that SAN-based tape libraries now have the capability to do "serverless" backup.
The backup server tells the E-Copy enabled device which data to back up and the device then moves the data directly from disk to tape. Since there is no server in the data stream, this backup method is known as "serverless."
So, now that you have the background the answer to your question is:
1. Third party copy = the device that USES "extended copy" to perform serverless backup.
2. Extended copy = The SCSI-3 command set that enables data movement between SAN devices.
For more information on the subject and to find information on the standards, go to SNIA and do a search for "x-copy." The SNIA workgroup on BACKUP is working with the extended copy stuff.
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This was first published in March 2003