Oracle® Solaris Cluster Concepts Guide

Exit Print View

Updated: July 2014, E39575-01

Global Devices

The Oracle Solaris Cluster software uses global devices to provide cluster-wide, highly available access to any device in a cluster from any node. In general, if a node fails while providing access to a global device, the Oracle Solaris Cluster software automatically uses another path to the device. The Oracle Solaris Cluster software then redirects the access to that path. For more information, see Device IDs and DID Pseudo Driver. Oracle Solaris Cluster global devices include disks, CD-ROMs, and tapes. However, the only multiported global devices that Oracle Solaris Cluster software supports are disks. Consequently, CD-ROM and tape devices are not currently highly available devices. The local disks on each server are also not multiported, and thus are not highly available devices.

The cluster automatically assigns unique IDs to each disk, CD-ROM, and tape device in the cluster. This assignment enables consistent access to each device from any node in the cluster. The global device namespace is held in the /dev/global directory. See Global Namespace for more information.

Multiported global devices provide more than one path to a device. Because multihost disks are part of a device group that is hosted by more than one cluster node, the multihost disks are made highly available.

Device IDs and DID Pseudo Driver

The Oracle Solaris Cluster software manages shared devices through a construct known as the 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 DID pseudo driver is an integral part of the shared device access feature of the cluster. The DID driver probes all nodes of the cluster and builds a list of unique devices, assigns each device a unique major and a minor number that are consistent on all nodes of the cluster. Access to shared devices is performed by using the normalized DID logical name, instead of the traditional Oracle Solaris logical name, such as c0t0d0 for a disk.

This approach ensures that any application that accesses disks (such as a volume manager or applications that use 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 Oracle Solaris device naming conventions as well. For example, Host1 might identify a multihost disk as c1t2d0, and Host2 might identify the same disk completely differently, as c3t2d0. The DID framework assigns a common (normalized) logical name, such as d10, that the nodes use instead, giving each node a consistent mapping to the multihost disk.

You update and administer device IDs with the cldevice command. See the cldevice(1CL) man page.