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Editor's note: experts receives many questions from its members on the subject of serverless backup. The three questions (and answers) below will tell you what serverless backup is, what the difference is between LAN-free backups and serverless backups, and what the best way is to design a server-free backup architecture.

Do you recommend using serverless backup?

First, let's define a few terms. LAN-free backup refers to multiple backup servers sharing tape drives. Their backups go across the SAN, not the LAN.

In client-free backup, I split off an additional mirror (or make a snapshot) that becomes visible to a server other than the server that originally used the data (usually the backup server). Then I back up that server via that other server. The data travels from disk, through the backup server, to tape and does not travel through the client. Thus, the term client-free.

Server-free backup: Same split mirror/snapshot as above but the data is sent directly from tape to disk and doesn't go through another server of any kind. Examples include the SCSI extended copy (XCOPY) command that can send data through the SAN from disk to tape, without going through a server or NDMP that can send data directly from the NAS filer to its tape drives without going through another server.

True serverless backup can help companies do things that are simply not possible any other way. But it does add a significant level of complexity and cost though, so you need to exhaust your other choices before going down that road. Make sure you've tried LAN-free backup and client-free backup first.

W. Curtis Preston

What is the difference between LAN-free backup and serverless backup?

LAN-free backup usually involves the ability to share a SAN connected tape library between all the nodes connected in the SAN. The backup server simply coordinates access to the tape resources. Each server in the SAN actually runs a copy of the backup engine and moves its own data to tape. This is sometimes called the "SSO" or shared storage option from some backup vendors. The backup server becomes the traffic cop for the SAN connected tape resources and allows each server in the SAN to back up its own data. This removes the need to "PULL" data over the LAN via backup agents to a backup server connected tape resource.

Serverless backup is accomplished by the backup server having the ability to connect to storage on behalf of other hosts connected to the SAN and back up that host's storage on its behalf. This usually involves the use of snapshot or image copies of the production LUNs in the SAN. The snapshot is used as the source media for backup so that the production application can continue during backup. The snapshot is given access through LUN security in the SAN for access by the backup server,and the backup server sends the data to tape.

Another method is to use the SCSI extended copy command called E-Copy which allows even the backup server to get out of the backup path. E-copy allows data to move directly from disk to tape via a "data router" which provides the E-copy intelligence.

Chris Poelker

I'm planning on implementing a SAN with two or more servers (W2K3 clustered) and using a serverless backup (tape library) architecture. What would be the best way to design this? What hardware would be needed?

In my book Storage Area Networks for Dummies, there is a chapter with diagrams on simple backup solutions using FC-AL hubs and shared tape drives. You don't need expensive software for a simple solution like this either. You can simply alternate access between the cluster nodes for backup, using the integrated Windows backup utility.

Since you are going to be using a cluster, you will require shared disk for the application resources (this can be a simple shelf of FC-AL based drives through a hub) and an HBA in each server for disk and another for tape (connected to another hub).

This should not run you more than a few grand to implement. Remember: When using hubs, always keep the disk traffic separate from the tape traffic by using dedicated loops for each.

Chris Poelker

For more information:

Tip: Do you want server-free or LAN-free backup?
Tip: Serverless backup is great but adds a level of complexity
Tip: Do the server-free two-step
This was last published in May 2004
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