Hot spare protection concepts

Hot spare disk units are spare disk units stored on a system to replace failed disks in case a disk failure occurs.

Hot spare disk units can be used to protect both device parity protected disk units and mirror-protected disk units.

A hot spare disk unit is stored on the system as a non-configured disk. When a disk failure occurs, the system exchanges the hot spare disk unit with the failed disk unit.

For device parity protected disk units, the hot spare disk unit must be the same capacity as the failed disk unit for a Small Computer System Interface (SCSI) IOA, or the same or larger capacity for a Serial Attached SCSI (SAS) IOA. The hot spare disk unit must also be under the same IOA in order for the exchange to occur. After the exchange occurs, the system rebuilds the data on the new disk unit.

For mirror-protected disk units, the hot spare disk unit must be the same capacity as the failed disk unit in order for the exchange to occur. The exchange of a mirrored subunit with the hot spare disk unit does not occur until mirror-protection has been suspended for 5 minutes and the replacement disk has been formatted. After the exchange occurs, the system synchronizes the data on the new disk unit.

A hot spare disk unit can be created manually from non-configured disk units on your system to protect existing or future mirror-protected units and device parity protected units. You can select which disk units and how many become hot spares. Starting hot spare protection explains how to add hot spare disk units to your system. When this option is selected, you must determine if one or more hot spares are desired and which available units become hot spares. The number is based on the total number of disk units attached to the IOA and their capacity.

When using hot spare protection with device parity protection, the system can automatically select and configure the hot spare disk unit when you initially start device parity protection. Starting device parity protection with hot spare protection explains how to include hot spare disk units when starting device parity protection. When selecting this option, the system automatically determines if one or two hot spares are created and which disk units are selected based on the total number and capacity of disk units attached to the IOA. When dealing with complex configurations such as those with varying disk unit capacities attached to the same IOA, you can start hot spare manually as described previously instead of allowing the system to select the hot spare disk units.

Note: The hot spare disk units are not designated to any particular parity set. The hot spare disk unit protects the first failed disk unit that has parity protection, is the appropriate capacity for the hot spare disk unit, and is under the same IOA as the hot spare disk unit.