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

Disk Load Balancing
SCF Reference Manual for the Storage Subsystem—529937-007
8-3
Guidelines for All G-Series RVUs
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. For detailed guidelines about how to use the
PRIMARY command, see Swapping Processors for a Disk on page 7-24.
The disk processing load within each enclosure should be evenly balanced between
the processor pair in that enclosure. Assuming that each disk handles the same
processing load, each enclosure should have one processor managing half of the
primary disk processes and the other processor managing the other half. If one disk
has to support a heavier processing load, you need to primary fewer disks from that
processor.
Topology Branch Example for G06.11 and Later RVUs
The group 02 topology branch includes processors 2 and 3 in the group 02 processor
enclosure and the three I/O enclosures attached to it (groups 21, 22, and 23). In the
figure on the next page, the disk processes are configured as follows:
•
Processors 2 and 3 jointly own all SACS in the same topology branch (groups 02,
21, 22, and 23).
•
Processor 2 manages the primary disk processes using the shaded SACs and
disks.
•
Processor 3 manages the primary disk processes using the white SACs and disks.
•
For simplicity, four disks are shown connected to each communication bus. The
enclosure can have up to eight disks per bus (16 disks in each enclosure).