Introduction to RAID : RAID Components and Features : Copyback

Copyback

Copyback lets you copy data from a source drive into a destination drive that is not a part of the virtual drive. Copyback often creates or restores a specific physical configuration for a drive group (for example, a specific arrangement of drive group members on the device I/O buses). You can run Copyback automatically or manually.

Typically, when a drive fails or is expected to fail, the data is rebuilt on a hot spare. The failed drive is replaced with a new disk. Then the data is copied from the hot spare to the new drive, and the hot spare reverts from a rebuild drive to its original hot spare status. The Copyback runs as a background activity, and the virtual drive is still available online to the host.

Copyback is also initiated when the first SMART error occurs on a drive that is part of a virtual drive. The destination drive is a hot spare that qualifies as a rebuild drive. The drive that has the SMART error is marked as failed only after the successful completion of the Copyback. This situation avoids putting the drive group in Degraded status.

*NOTE  During Copyback, if the drive group involved in Copyback is deleted because of a virtual drive deletion, the destination drive reverts to an Unconfigured Good state or Hot Spare state.

Order of Precedence

In the following scenarios, rebuild takes precedence over Copyback:

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If a Copyback is already taking place to a hot spare drive, and any virtual drive on the controller degrades, the Copyback aborts, and a rebuild starts. Rebuild changes the virtual drive to the Optimal state.

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The Rebuild takes precedence over the Copyback when the conditions exist to start both operations. Consider the following examples:

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Hot spare is not configured (or unavailable) in the system.

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Two drives (both members of virtual drives) exist, with one drive exceeding the SMART error threshold, and the other failed.

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If you add a hot spare (assume a global hot spare) during a Copyback, the Copyback is ended abruptly, and Rebuild starts on the hot spare.