Hardware Disk Mark Hotspare
From OSNEXUS Online Documentation Site
Communicates with the hardware RAID/HBA controller to toggle marking/unmarking of the specified disk as a hot-spare. Disks marked as hot-spares within a RAID controller can only be used as a hot-spare for RAID units created by that controller. As such if a system has two or more RAID controllers each one will need one or more disks marked as hot-spares in order to get automatic healing of RAID units. Systems using fault-tolerant software RAID at the Storage Pool level using HBAs have no requirement to specify hardware RAID hot-spares and in such cases this section does not apply.
