Persistent Bind - Creating Consistent Tape Links Across SAN (Doc ID 1009374.1)

Last updated on OCTOBER 05, 2022

Applies to:

Goal

How do I create same tape (/dev/rmt/...) links on all my Solaris[TM] hosts?

How do I control which tape (/dev/rmt/...) link points to which device?

Problem Description

To simplify management of servers in SAN based data centers, the SAN Foundation Software stack in the Solaris[TM] OS dynamically detects devices in a SAN and builds associated /dev tree entries without the need to edit configuration files.

In most cases, this greatly simplifies SAN management. However, for tape devices, some system administrators would still like the ability to explicitly specify how /dev entries are created and to insure the /dev entries are identical across multiple servers on a SAN. The procedure given below describes how administrators can specify this tape binding in the Solaris OS while retaining the benefits of automatic discovery and addition for disk-based devices.

Background

The /dev/rmt directory contains links to physical devices under /devices for tape devices. Each tape LUN seen by the system is represented by 24 minor nodes in the form of /dev/rmt/<N>, /dev/rmt/<N>b, /dev/rmt/<N>bn where N is an integer counter starting from 0. This number is picked by devfsadm during enumeration of new devices. Every new tape LUN found by devfsadm gets the next available number in /dev/rmt.

Since the /dev/rmt name is dependent upon the order in which devices appear in the device tree, it changes from host to host i.e. For a given tape drive seen by two or more different hosts, the /dev/rmt link can be different on each of these hosts. This breaks the most common usage of NetBackup (SSO option). Also, if the drive is replaced the links change unless the vendor provides a way to retain the PWWN of the drive.

Solution