Sun Cluster 3.1 Concepts Guide

Device ID (DID)

The Sun Cluster software manages global devices through a construct known as the device ID (DID) pseudo driver. This driver is used to automatically assign unique IDs to every device in the cluster, including multihost disks, tape drives, and CD-ROMs.

The device ID (DID) pseudo driver is an integral part of the global device access feature of the cluster. The DID driver probes all nodes of the cluster and builds a list of unique disk devices, assigning each a unique major and minor number that is consistent on all nodes of the cluster. Access to the global devices is performed utilizing the unique device ID assigned by the DID driver instead of the traditional Solaris device IDs, such as c0t0d0 for a disk.

This approach ensures that any application accessing disks (such as a volume manager or applications using raw devices) uses a consistent path across the cluster. This consistency is especially important for multihost disks, because the local major and minor numbers for each device can vary from node to node, thus changing the Solaris device naming conventions as well. For example, node1 might see a multihost disk as c1t2d0, and node2 might see the same disk completely differently, as c3t2d0. The DID driver assigns a global name, such as d10, that the nodes would use instead, giving each node a consistent mapping to the multihost disk.

You update and administer Device IDs through scdidadm(1M) and scgdevs(1M). See the respective man pages for more information.