AMCC 720-0138-00 manual About Degraded Units, About Inoperable Units

About Degraded Units

About Degraded Units

Fault tolerant RAID units provide data redundancy by duplicating information on multiple drives. These RAID units make it possible to continue use even if one of the drives in the unit has failed.

•RAID 1 and 10 units each use mirroring to achieve fault tolerance. Identical data is stored on two or more drives to protect against drive failure.

•RAID 5 units achieve fault tolerance by using a simple (exclusive OR) function to generate the parity data that is distributed on all drives.

When one of the drives in a fault-tolerant unit fails or is removed or unplugged, the unit is said to be degraded.

You can still read and write data from a degraded unit, but the unit will not be fault tolerant until it is rebuilt using the Rebuild feature.

When a RAID unit becomes degraded, it is marked as such, and the drive(s) that failed are marked as Degraded in the 3DM pages. On the 3ware Sidecar, the LED for failed drives turns red.

You should replace the failed drive and rebuild the unit as soon as it is convenient to do so. The unit will not be fault tolerant until it has been rebuilt. Rebuilding can occur automatically, depending on your settings. For more information, see “Rebuilding Units” on page 73.

Rebuilding Units

About Inoperable Units

Units become inoperable when there are no longer enough drives in the unit for it to function. For example, a RAID 5 created from 4 drives becomes degraded if one drive fails or is removed, but becomes inoperable if two drives fail or are removed.

Data on an inoperable unit cannot be accessed.

If you have data on a unit that is currently “inoperable,” contact technical support.

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