Dell PowerVault DL2000 - Manual (Page 14)

About hot spares in the Storage Provisioning Option
A hot spare is a physical disk that logically takes the place of any physical disk
that fails in a striped with parity disk group. You should specify a hot spare that
is at least the same size as the physical disk with the least capacity in each disk
group. The DL Appliance cannot rebuild a virtual disk with a hot spare that has
a capacity that is less than the smallest physical disk.
Note: In a standard configuration, each DL Appliance enclosure supports one hot
spare. Slot 0 is used to reserve one physical disk as a hot spare for storage array
fault tolerance purposes. If you use additional slots for hot spares, the DL Appliance
configuration state changes from standard to advanced.
If a physical disk fails, the DL Appliance automatically rebuilds the disk group by
logically including the hot spare in the rebuilt disk group. After you replace the
failed physical disk, the disk group is again rebuilt to include the new physical
disk. Data that is written on the hot spare is copied back to the virtual disk, which
includes the new physical disk. After the copy operation completes, the physical
disk in Slot 0 again becomes a hot spare.
Note: During a disk group rebuild operation, the DL Appliance is in a degraded
operational state, which affects system performance.
Introducing the Dell™ PowerVault™ DL Backup to Disk Appliance and the Backup Exec Storage Provisioning Option
About hot spares in the Storage Provisioning Option 14