Do you want server-free or LAN-free backup?

Characteristics, pros and cons.

Even though the terms have been commonly used for several years, there is still some confusion between LAN-free and server-free backup. In part this is because server-free backup is seen as a 'hotter' technology that promises better performance, so vendors want to refer to their approach as 'server-free' backup.

Both approaches use high-speed connections, such as Fibre Channel, and both can significantly improve the performance of tape backups when compared to conventional backup approaches. LAN-free backup connects the tape backup subsystem to the disk subsystem by a direct connection such as Fibre Channel Arbitrated Loop. This high-speed connection can transfer data at much greater than LAN speeds. LAN-free backup is usually the less expensive approach, especially when existing hardware such as tape drives can be reused.

In server-less backup a separate device takes over the job of transferring the data from the disks to the tape over the high-speed link. In effect it adds a controller, such as a Fibre Channel router or a blade in a Fibre Channel switch, to the LAN-free backup system to handle the job of moving data. The server simply acts as an overall coordinator rather than issuing the commands to move the blocks or files itself. Server-less backup provides a performance improvement over LAN-free backup, but the incremental improvement is less than what is gained by going from conventional to LAN-free backup. Server-less backup is also more expensive and complex than LAN-free backup, although this can be mitigated by using a lower performance server, or even eliminating the tape server altogether by moving its remaining functions onto another server.

The big advantage of server-less backup over LAN-free backup is that the appliances (called 'data movers' generically) that handle the control function can stream data to multiple tape drives to increase backup speed greatly in large or complex installations.

ATTO Technology Inc has a white paper that discusses LAN-free and Server-free backup.

Crossroads Systems Inc. has a white paper "Titled Server-Free Backup: Under The Covers" which explains the functions of file system management involved in backup.

Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.


This was first published in March 2003

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