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By Paul Ferrill

One of the storage innovations coming with both Windows 8 and Windows Server 2012 is something Microsoft calls offloaded data transfers, or ODX for short. It's really one of those things you wonder why somebody didn't think of sooner. In a nutshell, it takes advantage of new functionality for moving or copying data resident on a storage subsystem. This new functionality has its roots in the T10 XCOPY Lite specification, meaning Microsoft is using an existing standard for implementation as opposed to some proprietary capability.

Traditional file copy commands use local memory and network bandwidth for any files not located on an attached disk. That's true even if both source and target are located on the same network storage device. For this case, the system executing the copy must perform the moving of the data from one location to another, so every byte of the source file must travel over the network twice, both to and from the host computer. With ODX, the actual copying of the data is handled by the storage system and will not add any additional traffic to the primary network.

It's not hard to see how this type of operation would be easily supported by a storage area network (SAN) with a controller handling the distribution of data to various storage subsystems. With the first release of this technology you'll need a SAN as the back-end storage system. Having said that, ODX does function from both physical and virtual servers targeted at physical, virtual or SMB shared disks.

The improvements in network utilization are dramatic and can be significant in certain copy-intensive workloads. Dell has published some preliminary test results showing copy improvements in terms of time in the 3X range while host CPU utilization reduced by 36 percent and network bandwidth dropped to practically nothing. Creating and provisioning virtual machines is one such workload where this type of scenario would be common.

It's probably worth mentioning at this point that VMware has been providing a similar capability they call vSphere Storage APIs for Array Integration (VAAI) for some time. With the release of vSphere 5.0 they are now using the same T10 SCSI standard for all offload commands. Microsoft's ODX feature brings this capability up to the base operating system, so you'll be able to take advantage of any ODX-capable device with any file operations.

To make this work in a multi-server, multi-storage scenario, you must have a single copy manager acting as the traffic cop for all ODX operations. At Microsoft's TechEd event they teamed up with Dell, HP, IBM and NetApp to demonstrate ODX-capable storage systems running in conjunction with the Windows Server 2012 Release Candidate. There was a good session covering ODX titled Windows Server 2012 + Advanced Storage Solutions = Datacenter Elevation.

If you're really interested in this topic, you'll want to follow the server and management team's blog and check out this whitepaper on the Microsoft MSDN site.

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