You can save a ton of bandwidth by using Multicast with WDS. Multicast allows a server to send out a stream of data. Each machine “listening” to that stream can latch onto that stream. This allows for the Multicast server to send a single data stream out while multiple machines listen in and copy that data.
Say for example a WDS server has to stream a 4GB .wim file to each machine. If you didn’t use Multicast it would need to send 4GB x The number of clients you are wanting to image.
If you used Multicast that server would only have to send out 4GB. This last statement is mostly true as long as you do a scheduled cast. If you do an automatic cast the number would be greater as each new machine that boots up after the first would have missed parts of the stream and the WDS server would have to re-stream the parts that were missed.
It is because of this I find that scheduling a multicast to be more efficient. I normally schedule the task to start transmission once all machines have finished the PXE boot.
This post is going to assume that you already setup WDS.
Please enter a descriptive name for the Multicast Transmission… Please see how I named my task.
Specify the install image
Here is where you can schedule the cast. If you have 10 machines. Put 10 machines in the Threshold. If you have 20 machines put 20 as the threshold. Doing this allows the server to wait until all machines have connected. It allows the server to send out a single stream which helps cut down on errors.
This last screen just lets you know how you configured the transmission.
Now that you have created the transmission you can start PXE booting the machines. The server will wait for the number of machines you specified in the wizard. What happens however if one of the brand new machines arrives dead and you only have X-1 machines?
If you right click the Multicast Transmission item you can select “Start” and this will force the multicast session to start.
One thing you could do in the previous version of WDS is you could select the network speed at which the images would stream at. To do this you would Right click the server:
Go to the Network Tab and select the speed that you would want WDS to use. If you changed this item it would only apply AFTER you restarted the WDS service.
In Windows 2008R2 and greater these options are greyed out. Microsoft recommends that you just leave it as so. However if you really must specify the speed at which the WDS server multicast streams you must make manual changes to the registry.
If you want to read the reasoning behind the changes I found an article that sums everything up nicely here: Microsoft Blog WDS