Configuring Dual-String Mediators

This section provides information and procedures to configure dual-string mediator hosts. Dual-string mediators are required for all Solaris Volume Manager disk sets that are configured with exactly two disk strings and two cluster nodes. The use of mediators enables the Sun Cluster software to ensure that the most current data is presented in the instance of a single-string failure in a dual-string configuration.

A dual-string mediator, or mediator host, is a cluster node that stores mediator data. Mediator data provides information about the location of other mediators and contains a commit count that is identical to the commit count that is stored in the database replicas. This commit count is used to confirm that the mediator data is in sync with the data in the database replicas.

A disk string consists of a disk enclosure, its physical drives, cables from the enclosure to the node or nodes, and the interface adapter cards.

The following table lists the tasks that you perform to configure dual-string mediator hosts. complete the procedures in the order that is indicated.

Requirements for Dual-String Mediators

The following rules apply to dual-string configurations that use mediators.

• Disk sets must be configured with exactly two mediator hosts. Those two mediator hosts must be the same two cluster nodes that are used for the disk set.

• A disk set cannot have more than two mediator hosts.

• Mediators cannot be configured for disk sets that do not meet the two-string and two-host criteria.

These rules do not require that the entire cluster must have exactly two nodes. Rather, only those disk sets that have two disk strings must be connected to exactly two nodes. An N+1 cluster and many other topologies are permitted under these rules.

How to Add Mediator Hosts

Perform this procedure if your configuration requires dual-string mediators.

1. Become superuser on the node that currently masters the disk set to which you intend to add mediator hosts.

2. Add each node with connectivity to the disk set as a mediator host for that disk set.

   phys-schost# metaset -s setname -a -m mediator-host-list

   -s setname

   Specifies the disk set name.

   -a

   Adds to the disk set.

   -m mediator-host-list

   Specifies the name of the node to add as a mediator host for the disk set.

   See the mediator(7D) man page for details about mediator-specific options to the metaset command.

Example 4–10 Adding Mediator Hosts

The following example adds the nodes phys-schost-1 and phys-schost-2 as mediator hosts for the disk set dg-schost-1. Both commands are run from the node phys-schost-1.

phys-schost# metaset -s dg-schost-1 -a -m phys-schost-1
phys-schost# metaset -s dg-schost-1 -a -m phys-schost-2

Next Steps

Check the status of mediator data. Go to How to Check the Status of Mediator Data.

How to Check the Status of Mediator Data

Before You Begin

Ensure that you have added mediator hosts as described in How to Add Mediator Hosts.

1. Display the status of the mediator data.

   phys-schost# medstat -s setname

   -s setname

   Specifies the disk set name.

   See the medstat(1M) man page for more information.

2. If Bad is the value in the Status field of the medstat output, repair the affected mediator host.

   Go to How to Fix Bad Mediator Data.

Next Steps

Go to How to Create Cluster File Systems to create a cluster file system.

How to Fix Bad Mediator Data

Perform this procedure to repair bad mediator data.

1. Identify all mediator hosts with bad mediator data as described in the procedure How to Check the Status of Mediator Data.

2. Become superuser on the node that owns the affected disk set.

3. Remove all mediator hosts with bad mediator data from all affected disk sets.

   phys-schost# metaset -s setname -d -m mediator-host-list

   -s setname

   Specifies the disk set name.

   -d

   Deletes from the disk set.

   -m mediator-host-list

   Specifies the name of the node to remove as a mediator host for the disk set.

4. Restore each mediator host that you removed in Step 3.

   phys-schost# metaset -s setname -a -m mediator-host-list

   -a

   Adds to the disk set.

   -m mediator-host-list

   Specifies the name of the node to add as a mediator host for the disk set.

   See the mediator(7D) man page for details about mediator-specific options to the metaset command.

Next Steps

Determine from the following list the next task to perform that applies to your cluster configuration. If you need to perform more than one task from this list, go to the first of those tasks in this list.

• To create cluster file systems, go to How to Create Cluster File Systems.

• To create non-global zones on a node, go to How to Create a Non-Global Zone on a Global-Cluster Node.

• SPARC: To configure Sun Management Center to monitor the cluster, go to SPARC: Installing the Sun Cluster Module for Sun Management Center.

• Install third-party applications, register resource types, set up resource groups, and configure data services. See the documentation that is supplied with the application software and the Sun Cluster Data Services Planning and Administration Guide for Solaris OS.