IBM-AUSTRIA - PC-HW-Support    30 Aug 1999

Recovery Procedures for DDD Drives

This section provides you with procedures for recovering from many different DDD scenarios. Topics include:

•  An Overview of Drive Replacement
•  Software Replace vs. Physical Replace
•  Using and Understanding the RAID Administration Log
•  First Actions to be Performed On Service Call with DDD Drives
•  Recovery Procedures When HSP is Present at Time of Failure
•  Recovery Procedures When HSP is Not Present at Time of Failure
•  Recovery From RAID Adapter Failure

An Overview of Drive Replacement

For the IBM SCSI-2 F/W PCI-Bus RAID Adapter and the IBM F/W Streaming RAID Adapter/A, you perform drive replacement via the RAID Configuration Utility. To begin, select Replace Drive and Rebuild Drive options under Replace/Rebuild on the RAID Configuration Main Menu. With this action, the RAID Adapter sends a start unit command to the drive. Once the drive starts successfully, the drive state changes from defunct (DDD) to either hot-spare (HSP) or offline (OFL). The drive state is HSP if an HSP has already taken over for this DDD drive. The drive state is OFL if no HSP drive was present when the drive went DDD. The logical drive will be in a critical state and a rebuild is necessary to bring this drive into the array as online (ONL). Once the rebuild completes successfully, the logical drive indicates OKY status.

Software Replace vs. Physical Replace

When the RAID Adapter communicates with the hardfile and receives an unexpected response the adapter will mark the drive defunct in order to avoid any potential data loss. For example, this could occur in the event of a power loss to any of the components in the SCSI RAID subsystem. In this case, the RAID adapter will err on the side of safety and will no longer write to that drive although the drive may not be defective in anyway.

Different circumstances warrant either a software replace or a physical replace, as discussed in the following bullets:

•  Using a software replace is recommended to try to recover data when multiple DDD  drives occur. In this situation, you may lose data on drives that are not actually  defective if you run a normal rebuild process.

    IF YOU USE THE WRONG ORDER WHEN YOU ATTEMPT A  SOFTWARE REPLACE, DATA CORRUPTION RESULTS.

•  You can perform a software replace for a DDD drive when a hot spare (HSP) is not  present in the system. In this situation, the software replace requires a rebuild of the  drive. During the rebuild, all sectors of the drive are rebuilt. Therefore, the drive is  tested very well. If a rebuild of the drive completes successfully, the drive does not  need to be physically replaced.
•  If a DDD drive has been replaced by an HSP, you should physically replace the DDD  drive. Under these circumstances, a software replace will only send a start unit  command to the drive. If the unit starts successfully, then the drive is seen as good by  the RAID Adapter. Just restarting a drive does not sufficiently test the drive.  Therefore, the drive should be physically replaced to ensure a good HSP drive is  present in the system.

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