Network-Based Unicast and Multicast Restores
The most recent version of ASR allows for both multicast and unicast restores when the source image is accessed over a network. Both operations can be performed by any Mac OS X computer and do not require Mac OS X Server. Previous versions allowed for only unicast operations. In a unicast restore, each Mac that is the target of the deployment establishes a separate connection to the server hosting the image and begins to copy it. Although this is an effective method, each workstation that connects places additional load on the server and the network’s bandwidth—reducing performance. As a result, unicast restores are typically efficient only when deploying to a handful of workstations.
Multicast restores broadcast the disk image a stream across a network or subnet. Workstations connect to the stream and begin copying the image at any point, wrapping around and copying the earlier parts of the image and any missed segments until they have copied the entire image. Because the data is being streamed to all workstations simultaneously, there is no difference in performance between a single workstation and 100 workstations when deploying using a multicast restore. The network or subnet on which the operation is being performed, however, will be flooded with multicast data, and any other traffic will be severely affected. Multicast restores with Apple Software Restore are the most efficient methods for deploying to large numbers of workstations. For more information on ASR’s multicast and network operations, see my Peachpit.com article on multicast ASR.