This is a cabinet for a RAID - a Redundant Array of Inexpensive Disks. There are upt to 10 harddisks behind the door. It doesn't matter if a disk dies because its information is also stored on the other disks. One just hotswaps the broken disk with a new one. After a while, the information will be restored and, of course, again redundantly.

This cabinet is about a foot wide and high. There's a second cabinet (just like it) stacked on it.