A global spare disk acts as a hot spare for all RAID groups in a storage device such as a NAS or a connected expansion unit. In normal conditions, the disk is unused and does not store any data. When a disk in any RAID group fails, the hot spare disk automatically replaces the faulty disk. QTS copies the data to the spare disk in a process called RAID rebuilding.
Storage enclosures (the NAS and connected expansion units) cannot share global spare disks. A unique global hot spare disk must be assigned to each storage enclosure.
The disk appears as a green Spare on the Disks/VJBOD screen.