In this chapter we will be discussing the Device Request Dispatcher cluster subsystem. The Device Request Dispatcher, as I am sure you have probably already guessed, is the subsystem that dispatches requests to devices. Actually, it dispatches I/O requests to any storage device in the cluster (in fact there are some engineers within Compaq who prefer the name DeviceIO Request Dispatcher). The DRD also enables a cluster-wide view of all storage devices connected to any and all members of the cluster. The storage devices can be located on any bus on any system in the cluster; and not just shared buses private buses are also handled by the DRD. The DRD does not discriminate; any storage device is fair game. And the really great thing is that the DRD does all of this transparently from the user's perspective.

You may be starting to see a trend here. Every member can see all the file systems, every member can see all the devices (even those on a private bus), and everything is accomplished transparently. Not only will your users not require special training to use the cluster, they don't even have to know that they're using a cluster! With few exceptions, the goal is for all the cluster members to cooperate such that users see the cluster as simply one system.