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June 23, 2009


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David Magda

Isn't sending data from the media on which it lives to the back up media, without having to go through the network, what NDMP is / was supposed to do?

Scott Waterhouse

David... yes it is. Unfortunately, NDMP only works for filers (EMC Celerra and NetApp primarily) and carries some unfortunate legacy baggage in terms of how it defines backups (level 0, level 1, etc.). It doesn't work on just any old storage device, and probably isn't really well suited to backup of structured data sets. Lately it has been forced to do some weird things too--OST, anybody? At the end of the day, I guess I would have to chat to somebody that understands the guts of the protocol a lot better than I to see if it could be generalized to suit the purpose I describe above, or not. My suspicion is that it might be better to start again, but that is mostly a WAG.

Tommy Hueber

This is known within Tivoli Storage Manager (TSM) as a LAN-free backup. The component used for this, the Storage Agent, has been around now for years. The actual data is copied over the SAN infrastructure (storage to backup target) and the metadata flows over the LAN. An entire RedBook (along with the picture you've drawn above) is written about this subject. Maybe you'll want to look into this and you'll see some similarities with your story.

Scott Waterhouse


The LAN-free client is still only half way there to what I describe. With a LAN-free client, the data path still includes the application server; so in my diagram above the data would follow the path: #3 --> #2 --> #4. From a TSM server perspective, you do get the benefit that it only has to deal with meta-data, but the application server still has to bear an I/O load as well as generate meta-data. There are analogues for NetBackup and NetWorker in a SAN Media Server and a Dedicated Storage Node. But again, these are only half way to where we could go.

I apologize if I confused the issue by using network to describe both FC and IP connections. I did it deliberately because I feel that at some point we are going to have a converged network, and it was just simpler to discuss the issue in those terms.

Tommy Hueber

Scott, you're correct. Data movement directly from #3 to #4 is known as server-free and needs some sort of 'data mover'.

Joe Pfeiffer

NetBackup RealTime does what you describe as well in terms of 1-traverse of the network. When you first turn RealTime on it does a 3rd party SAN copy from the storage array to another storage array without going through the host - just storage to storage. Then the changes the host makes are just tracked in a journal after the initial mirror/sync which is also only 1-traverse (two if you count it for each array it goes to). That journal + the intial mirror allows for any-point-in-time recovery. Being a part of NetBackup also allows the use of the NBU app agents to do transaction consistant bookmarks where no data is sent (0-traverse!), just a time stamp is inserted in to RealTime. You could also do off-host backups to a backup app like NBU, NetWorker or TSM where additional copies are made to tape or disk - although it would do a 2-traverse across the network since the backup app media server reads the data.

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