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

4. The disk process, still executing in processor 2, attempts to access $D0203-M.
The path to $D0203-M on the Y fabric leads through SAC 1. This SAC is now owned by
processor 3. Because the disk process is executing in processor 2 but the SAC is owned by
processor 3, the disk access fails.
The disk process changes paths and tries to access $D0203-MB.
The path to $D0203-MB on the X fabric leads through SAC 1. Because this SAC is still owned
by processor 2 the disk access succeeds.
This process affects all disk processes that use these SACs.
NOTE: Loss of SAC ownership is detected only when an I/O is attempted. When ownership of
both SACs is lost, a read from one or both paths detects a loss of ownership. However, a read
from one path whose SAC ownership was not lost would not detect the loss of ownership of the
SAC on the path to the other disk.
Establishing a Disk Load Balance in RVUs Prior to G06.11
In RVUs prior to G06.11, you can simplify disk load balancing if you first establish a starting point
for SAC ownership so you know the owner of all SACs.
You enforce SAC ownership by using the PRIMARY DISK, FORCED command, which produces
this behavior:
• A specified disk primary process must run in the specified processor.
• All SACs that are used to access the disk become owned by that processor.
• All disk processes using those SACs must use that processor.
• Force all mirrored disks in the group 02 topology branch to run in processor 2:
-> PRIMARY $D02*, 2, FORCED
1. Change SAC ownership for all group 02 disks to processor 2:
-> INFO DISK $D02*, LABEL
2. Again swap the processors for these same disks, this time to processor 3:
-> PRIMARY $D0201, 3, FORCED
3. Change SAC ownership to processor 3:
-> INFO DISK $D02*-*, LABEL
4. If you want all these disks to run in processor 2, enter one final PRIMARY command:
-> PRIMARY $D02*, 2, FORCED
5. Change SAC ownership to processor 2:
-> INFO DISK $D02*, LABEL
6. The status shows all primary processes in processor 2:
-> STATUS $D02*-*
STORAGE - Status DISK \WAGER.$D0201-*
LDev Path Status State Substate Primary Backup
PID PID
104 PRIMARY ACTIVE STARTED 2,107 3,35
104 BACKUP INACTIVE STARTED 2,107 3,35
104 MIRROR ACTIVE STARTED 2,107 3,35
104 MIRROR-BACKUP INACTIVE STARTED 2,107 3,35
STORAGE - Status DISK \WAGER.$D0203-*
LDev Path Status State Substate Primary Backup
PID PID
130 Disk Load Balancing