CDP -- Continuous data protection (sometimes over a LAN)
Snapshot -- Disk based snapshots (software- or hardware-based)
Xcopy -- SCSI Xcopy disk-to-tape or disk-to-disk
BCV -- Hardware-based clones
Some methods require participation and licenses on the server being backed up, (LAN-less) some do not require the server that's LUNs are being backed up (server-less) and some do not even require a backup server (array-based backup).
Traditional backup requires the server being backed up to participate in the process, since the server would need to be aware that a backup was in process, and data writes should be quiesed. Usually the backup software would communicate with an agent (over IP) on the server, and the server would then ship data across the network to the backup server, which would then output the data to tape.
LAN-less backup lets you move the backup data stream off the corporate LAN, and redirect it through the SAN. LAN-less backup improves backup performance dramatically. A typical 10 megabit per second (Mbps) LAN can move backup data at around 1 megabyte per second (MBps). A SAN can move data at 100 MBps to 400 MBps (depending on the fabric speed). LAN-less backup may use the LAN for simple control information only. The actual backup data stream is re-directed over the SAN.
These figures are from chapter 9 of my book "Storage Area Networks for Dummies", which also covers snapshot backups and some formulas you can use for figuring out tape requirements and how long backup will take.
This was first published in January 2006