The 73GB SAS Drive Module for Xserve from Apple is a hot-pluggable spare hard drive for the Xserve. It can be used to add storage to an Xserve that does not have a full complement of drives or to use as a spare drive in the event of a drive failure. System administrators should always have at least one spare drive on hand to minimize downtime in the event of a drive failure.
Expanded Storage
You can use the drive module to expand the storage in your Xserve if there are open drive bays available. It can also be used to replace a failed drive.
Hot Pluggable
The drive is hot pluggable, allowing you to replace a bad drive or add capacity without having to power down your Xserve. This eliminates the downtime that is often associated with hardware upgrades or replacement, making your job as a system administrator easier.