Sun Cluster Concepts Guide for Solaris OS

Multi-Initiator SCSI

This section applies only to SCSI storage devices and not to Fibre Channel storage that is used for the multihost devices.

In a standalone (that is, non-clustered) host, the host controls the SCSI bus activities by way of the SCSI host adapter circuit that connects this host to a particular SCSI bus. This SCSI host adapter circuit is referred to as the SCSI initiator. This circuit initiates all bus activities for this SCSI bus. The default SCSI address of SCSI host adapters in Sun systems is 7.

Cluster configurations share storage between multiple hosts, using multihost devices. When the cluster storage consists of single-ended or differential SCSI devices, the configuration is referred to as multi-initiator SCSI. As this terminology implies, more than one SCSI initiator exists on the SCSI bus.

The SCSI specification requires each device on a SCSI bus to have a unique SCSI address. (The host adapter is also a device on the SCSI bus.) The default hardware configuration in a multi-initiator environment results in a conflict because all SCSI host adapters default to 7.

To resolve this conflict, on each SCSI bus, leave one of the SCSI host adapters with the SCSI address of 7, and set the other host adapters to unused SCSI addresses. Proper planning dictates that these “unused” SCSI addresses include both currently and eventually unused addresses. An example of addresses unused in the future is the addition of storage by installing new drives into empty drive slots.

In most configurations, the available SCSI address for a second host adapter is 6.

You can change the selected SCSI addresses for these host adapters by using one of the following tools to set the scsi-initiator-id property:

You can set this property globally for a host or on a per-host-adapter basis. Instructions for setting a unique scsi-initiator-id for each SCSI host adapter are included in Sun Cluster 3.1 - 3.2 With SCSI JBOD Storage Device Manual for Solaris OS.