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What is it and what does it do?
Xgrid is Apple’s clustering technology built into Mac OS X.
Xgrid can speed up a batch conversion by dealing out a video to each available CPU on
your network for conversion.
When you have more than one video in the file list and then check the "Enable Xgrid
Encoding" checkbox, VisualHub will enlist the help of any Macs on your local network that
have Xgrid enabled to distribute the load of batch encoding. If you have a multi-processor Mac,
Xgrid may also speed up the encoding process, with each processor working on a different video.
For example, a PowerMac G5 Quad under normal circumstances will only convert one video at a time, leaving anywhere
from 2.5 to 3 of its processors idle. With Xgrid, the same computer can utilize all 4 processors to their highest capacity.
How does it work?
There are two different types of Xgrid-enabled computers: Controllers and Agents.
The Controller is the computer responsible for telling the Agents what to do and to collect completed files. The
computer running VisualHub is the Controller. Controllers must be running 10.4 (Tiger) or higher and connected to a
network.
Agents take orders from the Controller and do the grunt work of video compression. Agents must be running 10.3.9
(Panther) or later and connected to the same network as the Controller. An Xgrid process running on an Agent will not
adversely affect the use of that computer; Xgrid processes always run at very low priority.
A Controller can also be an Agent to itself. You’ll see later how that can be a very good thing.
When you start an Xgrid-enabled batch, the Controller will do all the necessary detection and decision of settings for
each video, one by one. That information is sent to the Xgrid to await assignment. When an Agent is available, the Xgrid
will submit that information along with the video to be converted over the network to an Agent. Once all videos are sent
to the Xgrid, VisualHub will wait to hear back from Agents with completed videos. The progress bar will update for every
completed video. Once all videos are received, VisualHub will execute any post-conversion routines it normally does.
How do I set it up?
When Xgrid is enabled for the first time (by clicking on the
“Enable Xgrid Encoding” checkbox in the main window,
you will be prompted to start the Xgrid Controller. This is a
one-time action requiring an administrator’s password. A
tweak is also made to the number of processes that can run
at any given time, as Xgrid may spawn more than 100
background processes.
You will also have to set up each Xgrid Agent.
Tiger Agents: Go to the Sharing Preference Pane in System
Preferences. You will see a checkbox labeled Xgrid. If you
select the checkbox, the system will prompt you to edit the Xgrid settings. Click the “Configure” button to make these
changes. Use the settings in the screenshot to set up your Agent. For added security, you can have the Agents only
accept orders from a specific controller.
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