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

Correspondingly, if $OPER on the PMF CRU in slot 55 is balanced between X and Y, the primary
(-P or -B) disk OR the mirror (-M or -MB) disk has an asterisk:
Slot 55:
2 $OPER-M *STARTED 0,298 1,269
…
1 $OPER-B STARTED 0,298 1,269
However, these asterisks illustrate an unbalanced situation:
Slot 50:
2 $OPER-MB STARTED 0,298 1,269
…
1 $OPER-P STARTED 0,298 1,269
Slot 55:
2 $OPER-M *STARTED 0,298 1,269
…
1 $OPER-B *STARTED 0,298 1,269
Both halves of the mirrored volume are running on one fabric (in this case, the Y fabric).
To restore the balance between fabrics, switch the primary process to $OPER-P:
-> SWITCH $OPER-P
For detailed guidelines about how to use the SWITCH command, see “Changing the Active Path
for a Disk” (page 112).
Disk Load Balancing Between Processors
This subsection describes principles of disk load balancing between processors and how to achieve
an ideal balance. The technique for obtaining an ideal balance depends on the RVU:
RVU
“Guidelines for All G-Series RVUs” (page 119)
“Guidelines for G06.11 and Later RVUs” (page 119)
“Guidelines for G06.10 and Earlier RVUs” (page 123)
“PRIMARY Command Function in G06.00 Through G06.10” (page 125)
“PRIMARY Command Function in G05.00 and Earlier” (page 128)
Guidelines for All G-Series RVUs
Regardless of RVU:
• When you change a disk path or primary processor, the change does not actually take place
until the next I/O action on the disk.
• The active paths to any mirrored disk should be either the primary and mirror paths or the
backup and mirror-backup paths. This distribution ensures fault-tolerance because the disks
are accessed through separate system components.
• The same load-balancing principles apply to both internal disks and 45xx disks.
Most of the examples in this section use the naming conventions documented in the NonStop
S-Series Planning and Configuration Guide.
Guidelines for G06.11 and Later RVUs
• A processor can access any disk in its topology branch. Both processors in the processor
enclosure jointly own each SAC in each enclosure in the topology branch.
• The PRIMARY command specifies the processor in which the IOP should run its primary process;
it has no effect on the paths being used by other disk processes in the same topology branch.
Disk Load Balancing Between Processors 119