# Rebuilding a defunct drive

A physical drive is marked defunct when there is a loss of communication between the controller and the physical drive. This can be caused by any of the following:

- An improperly connected cable, physical drive, or controller
- Loss of power to a drive
- An improperly assembled SCSI channel in an unsupported configuration
- A defective cable, backplane, physical drive, or controller
- Connecting unsupported SCSI devices (such as tape drives or CD-ROM drives) to the same SCSI channel used for an array

In each case, after the communication problem is resolved, a rebuild operation is required to reconstruct the data for the device in its disk array. The ServeRAID controllers can reconstruct RAID level-1 and RAID level-5 logical drives. They cannot, however, reconstruct data stored in RAID level-0 logical drives because RAID level-0 is not redundant. If an array contains only RAID level-0 logical drives, the logical drives in the array are marked offline and the logical drives contain damaged data. You cannot rebuild the logical drives. You must correct the cause of the failure or replace the physical drives; then, you must restore your data.

To prevent data-integrity problems, the ServeRAID controllers set the RAID level-0 logical drives in the affected array to blocked during the rebuild operation for RAID level-1 or RAID level-5. After the rebuild operation is completed, you can unblock the RAID level-0 logical drives and access them once again. Remember, however, that the RAID level-0 logical drives contain damaged data.

Note:
  For logical drives in an IBM ServeRAID Cluster Solution:
  - Because shared logical drives can have only one logical drive for each array, blocking a RAID level-0 logical drive during a rebuild operation does not apply to shared logical drives.
  - Because non-shared logical drives can have more than one logical drive for each array, blocking a RAID level-0 logical drive during a rebuild operation does apply to non-shared logical drives.

## More information

- Recovering from defunct drives
- Rebuilding a hot-swap drive
- Changing the rebuild rate (action)
- Unblocking a logical drive (action)
- RAID level-0
- RAID level-1
- RAID level-5

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