Linux Clusters for the Mainstream Manager - Page 2
The cost benefit of clusters
The cost effectiveness of open source software is a no-brainer. "No one ever needs a cluster — but it is often the most cost effective way to get the job done," claims Dague, especially when coupled with Linux.
Clusters can be run on inexpensive PC hardware, as well as on Linux distributions operating on top of zOS- or OS390-driven mainframes.
But keep 'Hidden Costs' in mind, too
On the downside, however, clusters can be accompanied by some hidden costs, including:
- Administration costs – The increased cost of administration as clustering scales upward must be taken into account. How many administrators will it take to run 100 nodes? 1000 nodes?
- Facility costs – Large numbers of CPUs add a great deal of weight and heat to an installation. "Are you sure your building can handle the weight?" questions Dague. "AC (air conditioning) is critical."
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Tips and Tricks: Installation
Linux clustering is also a relatively new phenomenon, a fact that might help explain lingering reluctance by some businesses to get started.
Moreover, in some ways, Linux is still sort of a land unto itself. Methods of initial installation, for example, can vary from one Linux distribution to another.
For "lights out" installation, Dague recommends administrators use the following:
- Kickstart for Red Hat distributions
- AutoYast for SuSE distributions
- FAI for Debian distributions
"New machines must be brought from bare members of the cluster with minimal effort," says Dague. "CDs don't cut it."
What to do about 'version skew'
Software maintenance is another big issue. Sometimes, mass updates are performed on some nodes, while other nodes are down. Certain administrators apply hot fixes only to individual nodes that are in particular need of maintenance.
"Before long, though, it becomes unclear what [software] is on any given node," says Dague. Unless you keep careful documentation, this situation leads to "version skew."
Dague offers three options for staving off version skew:
Apply updates only as packages. Even if you're merely making configuration file changes, apply updates only as packages. That way, documentation will be "all in the packages."
Use imaging software such as System Installation Suite. With this approach, image and documentation are one and the same. "Make sure you back up the image, though," advises Dague. Otherwise, if you lose the image, the documentation will go down the drain, too. System Installation Suite is "distro-independent," he notes.
- Create a "diskless" environment. Run nodes off a network file system. All nodes attached to the file system will be running the same software versions. Under this scenario, too, backup is key.