About Rebuilds

Fault tolerant RAID units provide data redundancy by duplicating information on multiple drives.

RAID 1 and 10 units each use mirroring, where identical data is stored on two or more drives to protect against drive failure.
RAID 5 and 50 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 is removed, unplugged or fails on read or write requests, the unit is said to be "degraded." Rebuilding is the process by which the RAID unit is made fault tolerant again.

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.

In all cases, 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.

If a hot spare is specified and a redundant unit degrades, an event notification is generated and the hot spare automatically replaces the failed drive in the redundant unit without user intervention. The rebuild process will automatically be launched as a background process at the next scheduled time. If scheduling is turned off, the rebuild process will start almost immediately (within a couple of minutes). If 3DM is running and E-mail notification is enabled, an event notification will be sent to specified users when the rebuild process is complete.

For 9550SX and 9590SE controllers, if Auto-Rebuild is enabled, other drives in addition to spares may be used to rebuild degraded units. If no spare is available, the firmware will attempt to rebuild the unit using first any available drives and then any failed drives. This allows you to insert a new drive to use in the rebuild process.

With the 3ware 9000 series controller, rebuilds on multiple units can take place simultaneously.

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Related Topics

Rebuilding Units

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