Chapter 12. Specialized UML Configurations

So far we have seen UML instances with fairly normal virtual hardware configurationsthey are similar to common physical machines. Now we will look at using UML to emulate unusual configurations that can't even be approached with common hardware. This includes configurations with lots of devices, such as block devices and network interfaces, many CPUs, and very large physical memory, and more specialized configurations, such as clusters.

By virtualizing hardware, UML makes it easy to simulate these configurations. Virtual devices can be constructed as long as host and UML memory hold out and no built-in software limits are reached. There are no constraints such as those based on the number of slots on a bus or the number of buses on a system.

UML can also emulate hardware you might not even have one instance of. We'll see an example of this when we build a cluster, which will need a shared storage device. Physically, this is a disk that is some-how multiported, either because it is multiported itself or because it's on a shared bus. Either way, this is an expensive, noncommodity device. However, with UML, a shared device is simply a file on the host to which multiple UML instances have access.