Checking disks and disk adapters

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Use the diag command to verify that the adapter card is functioning properly. If problems arise, be sure to check the jumpers, cables, and terminators along the SCSI bus.

For SCSI disks, including IBM® SCSI disks and arrays, make sure that each array controller, adapter, and physical disk on the SCSI bus has a unique SCSI ID. Each SCSI ID on the bus must be an integer value from 0 through 15, although some SCSI adapters may have limitations on the SCSI ID that can be set. See the device documentation for information about any device-specific limitations. A common configuration is to set the SCSI ID of the adapters on the nodes to be higher than the SCSI IDs of the shared devices. Devices with higher IDs take precedence in SCSI bus contention.

For example, if the standard SCSI adapters use IDs 5 and 6, assign values from 0 through 4 to the other devices on the bus. You may want to set the SCSI IDs of the adapters to 5 and 6 to avoid a possible conflict when booting one of the systems in service mode from a mksysb tape of other boot devices, since this will always use an ID of 7 as the default.

If the SCSI adapters use IDs of 14 and 15, assign values from 3 through 13 to the other devices on the bus.

You can check the SCSI IDs of adapters and disks using either the lsattr or lsdev command. For example, to determine the SCSI ID of the adapter scsi1 (SCSI-3), use the following lsattr command and specify the logical name of the adapter as an argument:

lsattr -E -l scsi1 | grep id

Do not use wildcard characters or full pathnames on the command line for the device name designation.

Important: If you restore a backup of your cluster configuration onto an existing system, be sure to recheck or reset the SCSI IDs to avoid possible SCSI ID conflicts on the shared bus. Restoring a system backup causes adapter SCSI IDs to be reset to the default SCSI ID of 7.

If you note a SCSI ID conflict, see the Planning Guide for information about setting the SCSI IDs on disks and disk adapters.

To determine the SCSI ID of a disk, enter:

lsdev -Cc disk -H