NDMP was developed primarily to address the issue of storage management backup software vendors adapting to work with the various operating systems they support. The implementations had many operating system dependencies and required a great deal of support. The idea was to create a backup protocol (set of relationships and information to be transferred) between the backup applications, servers and backup devices.
In the case you are talking about, the network attached storage devices would have the capability to be NDMP compliant that means that the protocol for doing the backup is being handled by that device. Think of it as separating the command/control information from the data stream. The command/control information would flow between the requesting server running the backup software and the NDMP server (NAS box) but the data stream would go from the NDMP server to the storage device (usually a tape drive). There's a good explanation of this at http://www.ndmp.org/wp/wp.shtml.
The Microsoft Server Appliance Kit is just an optimized operating system that runs on Intel-based platform for purposes such as the base for NAS devices. NAS devices typically (but not in all cases) run on a system with a processor (or processors) with some embedded operating system and additional functions and features that are added by additional software. Network Appliance's operating system is called Data ONTAP for example. The SAK is really no different from a concept standpoint than that. Additional functions could be added. The specific vendor that used that OS can add the NDMP functionality.
So, using the SAK to compare against NDMP compliance is too gross a comparison. The comparison should be done on individual product offerings. The true issues to look at should be the functions provided regarding the value they bring to you, the administrative costs (both in set up and long term administration, the product costs, and whether the performance meets your requirements. Each product should be considered irrespective of the way it achieves these characteristics.
Evaluator Group, Inc.
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This was first published in October 2001