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:
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, level-1E, level-5, level-5E, level-5EE, level-10, level-1E0, and level-50 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.