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H-2 Recovering from Drive Failure

Writer: Rickard Project: Compaq Smart Array 3200 Controller Reference Guide Comments: 340862-002

File Name: O-APPH.DOC Last Saved On: 12/7/98 1:47 PM

COMPAQ CONFIDENTIAL - NEED TO KNOW REQUIRED

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.

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Compaq 3200 Especificaciones Pagina 182