Configuring Dual-String Mediators

This section contains the following information and procedures:

Requirements for Dual-String Mediators

A dual-string mediator, or mediator host, is a cluster node that stores mediator data. Mediator data provides information on the location of other mediators and contains a commit count that is identical to the commit count 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.

Dual-string mediators are required for all Solstice DiskSuite/Solaris Volume Manager disksets that are configured with exactly two disk strings and two cluster nodes. A disk string consists of a disk enclosure, its physical disk drives, cables from the enclosure to the node(s), and the interface adapter cards. 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. The following rules apply to dual-string configurations that use mediators.

Disksets must be configured with exactly two mediator hosts. Those two mediator hosts must be the same two cluster nodes that are used for the diskset.
A diskset cannot have more than two mediator hosts.
Mediators cannot be configured for disksets 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 disksets 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.

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

Run the metaset(1M) command to add each node with connectivity to the diskset as a mediator host for that diskset.
# metaset -s setname -a -m mediator-host-list
-s setname

Specifies the diskset name

-a

Adds to the diskset

-m mediator-host-list

Specifies the name of the node to add as a mediator host for the diskset

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

Check the status of mediator data.

Go to How to Check the Status of Mediator Data.

Example—Adding Mediator Hosts

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

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

How to Check the Status of Mediator Data

Add mediator hosts as described in How to Add Mediator Hosts.

Run the medstat command.
# medstat -s setname
-s setname

Specifies the diskset name

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

Is Bad the value in the Status field?
- If yes, go to How to Fix Bad Mediator Data to repair the affected mediator host.
- If no, go to How to Add Cluster File Systems to create a cluster file system.

How to Fix Bad Mediator Data

Perform this procedure to repair bad mediator data.

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

Become superuser on the node that owns the affected diskset.

Remove all mediator hosts with bad mediator data from all affected disksets.
# metaset -s setname -d -m mediator-host-list
-s setname

Specifies the diskset name

-d

Deletes from the diskset

-m mediator-host-list

Specifies the name of the node to remove as a mediator host for the diskset

Restore each mediator host that you removed in Step 3.
# metaset -s setname -a -m mediator-host-list
-a

Adds to the diskset

-m mediator-host-list

Specifies the name of the node to add as a mediator host for the diskset

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

Create cluster file systems.

Go to How to Add Cluster File Systems.