Managing Serviceguard 12th Edition, March 2006

Planning and Documenting an HA Cluster
Hardware Planning
Chapter 4140
Setting SCSI Addresses for the Largest Expected
Cluster Size
SCSI standards define priority according to SCSI address. To prevent
controller starvation on the SPU, the SCSI interface cards must be
configured at the highest priorities. Therefore, when configuring a highly
available cluster, you should give nodes the highest priority SCSI
addresses, and give disks addresses of lesser priority.
For SCSI, high priority starts at seven, goes down to zero, and then goes
from 15 to eight. Therefore, seven is the highest priority and eight is the
lowest priority. For example, if there will be a maximum of four nodes in
the cluster, and all four systems will share a string of disks, then the
SCSI address must be uniquely set on the interface cards in all four
systems, and must be high priority addresses. So the addressing for the
systems and disks would be as follows:
Table 4-1 SCSI Addressing in Cluster Configuration
System or Disk Host Interface SCSI Address
Primary System A 7
Primary System B 6
Primary System C 5
Primary System D 4
Disk #1 3
Disk #2 2
Disk #3 1
Disk #4 0
Disk #5 15
Disk #6 14
Others 13 - 8