Preparing I/O and Network Devices

A board with vital system resources cannot be detached unless alternate resources are available on another board. A boot disk is an example of a vital system resource.

A board hosting non-vital system resources can be unconfigured whether or not there are alternate paths to the resources. All of its file systems must be unmounted and its swap partitions must be deleted. You may have to kill processes that have open files or devices, or place a hard lock on the file systems (using lockfs(1M)) before unmounting them. All I/O device drivers must be detachable.

The system swap space should be configured as multiple partitions on disks attached to controllers hosted by different boards. With this kind of configuration, a particular swap partition is not a vital resource because swap partitions can be added and deleted dynamically. See swap(1M) for more information.

When memory or disk swap space is detached, there must be enough memory or swap disk space remaining in the machine to accommodate currently running programs.