Managing Serviceguard Eighteenth Edition, September 2010

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
Host Interface SCSI AddressSystem or Disk
7Primary System A
6Primary System B
5Primary System C
4Primary System D
3Disk #1
2Disk #2
1Disk #3
0Disk #4
15Disk #5
14Disk #6
13 - 8Others
NOTE: When a boot/root disk is configured with a low-priority address on a shared
SCSI bus, a system panic can occur if there is a timeout on accessing the boot/root
device. This can happen in a cluster when many nodes and many disks are configured
on the same bus.
The correct approach is to assign SCSI addresses in such a way that the interface cards
on cluster nodes have the highest priority SCSI addresses, followed by any boot/root
disks that are on the shared bus, followed by all other disks on the shared bus.
Disk I/O Information
Collect the following information for each disk connected to each disk device adapter
on the node:
Bus Type
Indicate the type of bus. Supported busses are Fibre Channel
and SCSI.
126 Planning and Documenting an HA Cluster