Replacing hard drives

If you are replacing a drive in a fault-tolerant configuration while the system is powered down, a POST message appears when the system is powered up. When this message appears, press the F1 key to enable automatic data recovery. If you do not enable automatic data recovery, the logical volume remains in a ready-to-recover condition, and the same POST message appears when the system is restarted.

In RAID 1 configurations, you can replace one failed drive.

In RAID 1+0 configurations, drives are mirrored in pairs. If drives are not mirrored to removed or failed drives, you can replace them simultaneously.

Guidelines

Before replacing hard drives, observe the following guidelines:

•Be sure that the array has a current, valid backup.

•Confirm that the replacement drive is a SATA drive.

•Use replacement drives that have a capacity equal to or greater than the smallest drive in the array. The controller immediately fails drives that have insufficient capacity.

To replace more drives in an array than the fault tolerance method can support, follow the previous guidelines for replacing several drives simultaneously. Wait until rebuild is complete, as indicated by ACU/ACU-CLI, before replacing additional drives.

If you need to replace more drives than the fault tolerance method can support because fault tolerance has been compromised, recover the data before replacing any drives. For more information, see "Recovering from compromised fault tolerance (on page 14)."

Automatic data recovery (rebuild)

When you replace a hard drive in an array, the controller uses the fault-tolerance information on the remaining drives in the array to reconstruct the data from the original drive and write it to the replacement drive. This process is called automatic data recovery or rebuild. If fault tolerance is compromised, this data cannot be reconstructed and, likely, is lost permanently.

If another drive in the array fails while fault tolerance is unavailable during rebuild, a fatal system error can occur, and all data on the array is then lost. In exceptional cases, however, failure of another drive does not always cause a fatal system error. These exceptions include the following:

•Failure after activation of a spare drive

•Failure of a drive that is not mirrored to any other failed drives (in a RAID 1+0 configuration)

Time required for a rebuild

The time required for a rebuild varies, depending on several factors:

•The priority that the rebuild is given over normal I/O operations

Change the priority setting with ACU ("Array Configuration Utility" on page 7).

•The amount of I/O activity during the rebuild operation

•The rotational speed of the hard drives

Replacing, moving, or adding hard drives 15