122 Configuration: Disk Groups and Virtual DisksHot Spares and RebuildA valuable strategy to protect data is to assign available physical disks in thestorage array as hot spares. A hot spare adds another level of fault tolerance tothe storage array.A hot spare is an idle, powered-on, stand-by physical disk ready for immediateuse in case of disk failure. If a hot spare is defined in an enclosure in which aredundant virtual disk experiences a physical disk failure, a rebuild of thedegraded virtual disk is automatically initiated by the RAID controllermodules. If no hot spares are defined, the rebuild process is initiated by theRAID controller modules when a replacement physical disk is inserted intothe storage array.Global Hot SparesThe MD3600f Series supports global hot spares. A global hot spare canreplace a failed physical disk in any virtual disk with a redundant RAID levelas long as the capacity of the hot spare is equal to or larger than the size of theconfigured capacity on the physical disk it replaces, including its metadata.Hot Spare OperationWhen a physical disk fails, the virtual disk automatically rebuilds using anavailable hot spare. When a replacement physical disk is installed, data fromthe hot spare is copied back to the replacement physical disk. This function iscalled copy back. By default, the RAID controller module automaticallyconfigures the number and type of hot spares based on the number andcapacity of the physical disks in your system.A hot spare may have the following states:• Standby hot spare—is a physical disk that is assigned as a hot spare and isavailable to take over for any failed physical disk.• In-use hot spare—is a physical disk that is assigned as a hot spare and iscurrently replacing a failed physical disk.
