SCF Reference Manual for the Storage Subsystem (G06.28+, H06.05+, J06.03+)

Reviving a Mirrored Disk
The “START DISK Command” (page 274) makes a stopped disk accessible to user processes and
revives the second half of a mirrored volume.
Use this procedure if you have stopped one half of a mirrored volume and need to synchronize
the two halves when restarting the disk. This situation can occur if:
• You do something that affects only one disk of a mirrored volume. For an example, see
“Replacing the Bootstrap Program” (page 107).
• You back up disk files by replacing the mirror drive with another drive instead of using BACKUP
and RESTORE.
• You are “Swapping Processors for a Disk” (page 109).
• One half of a mirrored pair experiences a physical media failure, and you have to stop and
remove it.
Considerations When Reviving a Mirrored Volume
• Do not stop the revive operation by issuing a STOP DISK command unless you want to force
the next revive operation to restart from the beginning. See “Stopping a Revive Operation”
(page 100).
• If a nonfatal error occurs, the revive operation does not proceed but stalls or goes into a loop.
The START DISK command continues to retry at the current address until either the revive
operation is successful or the revive operation is suspended or stopped. For more details, see
“Stopping a Revive Operation” (page 100).
• When SCF must revive the information on the volume before starting the volume, the revive
operation can seriously affect system performance, especially for users of the volume being
revived. You can use the RESET DISK command to temporarily suspend the revive operation
when needed. See “Temporarily Stopping a Revive Operation” (page 101).
Starting a Mirrored Disk
1. Verify the current state of the disk volume:
-> STATUS $DSMSCM-*
STORAGE - Detailed Status DISK \ALM171.$DSMSCM
Disk Path Information:
LDev Path Status State Substate Primary Backup
PID PID
98 PRIMARY ACTIVE STOPPED DOWN 0,21 1,15
98 BACKUP INACTIVE STOPPED DOWN 0,21 1,15
98 MIRROR ACTIVE STOPPED DOWN 0,21 1,15
98 MIRROR-BACKUP INACTIVE STOPPED DOWN 0,21 1,15
2. If all paths are not in the STOPPED state, substate DOWN:
-> RESET $DSMSCM
3. Start the disk process:
-> START $DSMSCM
The disk revive operation does the following:
a. The disk process copies the percentage of the total number or sectors that have been
specified by the REVIVERATE attribute from the disk with the newer timestamp to the disk
that is being revived (the disk with the older timestamp).
b. The disk process checks for other work to be done. If there are no other requests pending,
the disk process starts the disk revive operation again.
c. The disk process handles any waiting requests.
98 Managing Disks