Background
If your computers are identical or even just similar, you can greatly speed up the process of getting images delivered by using multicast.
Normally, the entire image is transferred from the imaging server to each client. If the image in question is 2 GB in size, and you have 25 workstations, at least 50 GB of data must be pushed over the network (more is required, because each packet of data must be acknoledged by each workstation).
With multicast, all the workstations to receive an image are syncronized, each packet of the image is sent only once. Once all stations acknoledge that they've successfully received the packet, the next is sent. In this manner, the duplicate transmission of the image data is avoided, with the potential to see orders of magnitude performance increases.
Zen Multicast
In the Zen imaging environment, you select one computer to be the imaging "master" The contents of the master's hard disk are transferred to the "client" workstations. The master's hard drive can be prepared by simply downloading a conventional image, or it can be customized with applications and data that you want to push to your client machines. If you customize a workstation, be sure to prepare it with MS Sysprep before you multicast it's hard drive to the clients. If you don't, then every client will end up with an exact copy of the master, including the same name and Windows Security ID numbers (SIDs).
Master computers and their clients do NOT need be on the same TCP/IP subnet. In order to match clients to the proper masters, a multicast "session name" is used.
By default, WolfPrep will generate a session name for you, based on the TCP/IP subnet. It uses the "broadcast address" of the workstation in this session name, which should be the same for all stations in the same subnet. In the case where all the machines are located in the same TCP/IP subnet, you can use this session name unchanged. If your multicast session is to include machines in multiple subnets, you'll have to override the session name to make sure the client machines have the same session name as the master.
Steps
Step 0: Download or prepare a computer to be the workstation master.
If you've downloaded an image and don't need to customize it, then DO NOT remove the CD-ROM when you reboot. Be certain that it is inserted and available to boot from. If you reboot from the hard drive, Sysprep will run and generate new SID numbers, which you don't want to happen just yet.
Step 1: Boot the master computer with WolfPrep imaging CD-ROM and enter
a command on the pre-boot menu like
multicast ROLE=master
This establishes a multicast session, and the computers role as the "master" station, using the automatically generated session name.
You can set other parameters on the pre-boot command line if you wish, or if the defaults satisfy you, go ahead and start the multicast clients.
The parameters you can set are:
| Option | Units | Description |
| SESSION= | The multicast session name to use. This can be any string, but it must be unique or clients will not be able to find their masters. One's login ID or a lab name make good session names | |
| ROLE= | master or client | The station who's hard drive should be copied to all the others should be set as the "master" All other machines are "client" |
| COUNT= | number of stations | If set, the master will automatically start once this number of clients have connected to the multicast session. |
| WAIT= | time in minutes | If set, the master will automatically start after this number of minutes have elapsed. |
When specifiy options on the pre-boot menu, remember that all options are case-sensitive (you must use ROLE=, not Role= or role=) and there must be no spaces around the equals signs.
Step 2: Boot the each client computer with the WolfPrep imaging CD-ROM and enter a command on the pre-boot menu like
multicast ROLE=client
You can shorten this to just "multicast" or even "mc"
If you are using a custom session name on the master (SESSION=) then you must use the exact same session name on each and every client machine.
The client machines will wait until the master starts the multicast session. This is either in response to commands from the master's keyboard (if no options were given on the master's command line) or after a timeout (if the master used WAIT=) or when a certain number of clients have been successfully started (if the master used COUNT=)
The master station will transfer it's hard drive to the client machines, which will then download any Plug and Play drivers they can detect. This extra PnP step should assure that even if machines are not identical they can successully use multicast.
After the img engine has completed, you will be prompted to eject the CD-ROM and reboot the workstation. You can reboot by either issuing the linux command "reboot" pressing CONTROL+ALT+DELETE or using the machine's power button.
When each workstation is rebooted, it will run the WolfPrep script process to
register the workstation and apply any updates needed.
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