Compaq 3200 manual Fault Tolerance and Drive Failure, A Non-Fault-Tolerant RAID 0 Logical Drive

H-2Recovering from Drive Failure

Fault Tolerance and Drive Failure

In the event of a drive failure, the condition of the logical drive varies, depending upon the fault-tolerance method used. Since a single array of physical drives can contain multiple logical drives with different fault-tolerance methods, conditions of each logical drive on the same array are not necessarily the same. At any one time, if more drives are failed than the fault-tolerance method allows, fault tolerance is “compromised” and the condition of the logical drive can be referred to as “failed.” If a logical volume is “failed,” all requests from the operating system will be rejected with “unrecoverable” errors.

A Non-Fault-Tolerant (RAID 0) Logical Drive

A Non-Fault-Tolerant (RAID 0) logical drive can sustain no drive failures. If any physical drive in the array is failed, the condition of all non-fault-tolerant logical drives in the same array will also be “failed” because data is striped across all drives in the array.

A RAID 1 (Mirroring) Logical Drive

■Can sustain multiple drive failures as long as failed drives are not mirrored to one another

■Will be in a “failed” condition if any two failed drives are mirrored to one another

■Will be in a “regenerating” condition if at least one drive is failed and no failed drives are mirrored to one another

■Will be in a “rebuilding” condition if a previously failed drive has been replaced and the replacement drive is rebuilding. The volume may also be in a “rebuilding” condition following a drive failure if a spare drive was previously assigned and is being rebuilt.

In any RAID 1 logical drive on the Smart Array 3200 Controller tht has N physical drives in the array (not including spare drives), the first N/2 physical drives are normally mirrored in consecutive order to the second N/2 physical drives. When determining the order, number each drive in the array by increasing IDs on the first SCSI bus, followed by drives on the second SCSI bus.