SCF Reference Manual for the Storage Subsystem (G06.24+, H06.03+)

Disk Load Balancing
SCF Reference Manual for the Storage Subsystem—529937-007
8-13
PRIMARY Command Function in G05.00 and Earlier
$D0203 changes paths to access the disk in because:
1. The disk process executing in processor 2 attempts to access $D0203-P.
The path to $D0203-P on the X fabric leads through SAC 2. This SAC is now
owned by processor 3. Because the disk process is executing in processor 2, the
disk access fails.
2. The disk process changes paths and tries to access $D0203-B.
The path to $D0203-B on the Y fabric leads through SAC 2. Because this SAC is
still owned by processor 2, the disk access succeeds.
3. 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.
4. 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.
-MB
-B
-M
-P
-P
-M-MB
-B
-B
Processor 2
X Y
SCSI Bus 2
SAC 1 SCSI Bus 1 SAC 1
SAC 2
SAC 2
Processor 3
X Y
X Y
-MB -M
-P -B -P -B
-P
$D0201-M
$D0203-M $D0205-M $D0208-P
$D0201-P $D0203-P $D0205-P $D0207-P
VST511.vsd
$D0201
$D0203'
$D0205'
$D0207'
$D0208'
$D0201'
$D0203
$D0205
$D0207
$D0208