Sun Cluster Concepts Guide for Solaris OS

Disk-Path Monitoring

The current release of Sun Cluster software supports disk-path monitoring (DPM). This section provides conceptual information about DPM, the DPM daemon, and administration tools that you use to monitor disk paths. Refer to Sun Cluster System Administration Guide for Solaris OS for procedural information about how to monitor, unmonitor, and check the status of disk paths.

Note –

DPM is not supported on nodes that run versions that were released prior to Sun Cluster 3.1 10/03 software. Do not use DPM commands while a rolling upgrade is in progress. After all nodes are upgraded, the nodes must be online to use DPM commands.

DPM Overview

DPM improves the overall reliability of failover and switchover by monitoring the secondary disk-path availability. Use the scdpm command to verify availability of the disk path that is used by a resource before the resource is switched. Options that are provided with the scdpm command enable you to monitor disk paths to a single node or to all nodes in the cluster. See the scdpm(1M) man page for more information about command-line options.

The DPM components are installed from the SUNWscu package. The SUNWscu package is installed by the standard Sun Cluster installation procedure. See the scinstall(1M) man page for installation interface details. The following table describes the default location for installation of DPM components.





Command-line interface 


Share libraries 


Daemon status file (created at runtime) 


A multithreaded DPM daemon runs on each node. The DPM daemon (scdpmd) is started by an rc.d script when a node boots. If a problem occurs, the daemon is managed by pmfd and restarts automatically. The following list describes how the scdpmd works on initial startup.

Note –

At startup, the status for each disk path is initialized to UNKNOWN.

  1. The DPM daemon gathers disk-path and node name information from the previous status file or from the CCR database. Refer to Cluster Configuration Repository (CCR) for more information about the CCR. After a DPM daemon is started, you can force the daemon to read the list of monitored disks from a specified file name.

  2. The DPM daemon initializes the communication interface to answer requests from components that are external to the daemon, such as the command-line interface.

  3. The DPM daemon pings each disk path in the monitored list every 10 minutes by using scsi_inquiry commands. Each entry is locked to prevent the communication interface access to the content of an entry that is being modified.

  4. The DPM daemon notifies the Sun Cluster Event Framework and logs the new status of the path through the UNIX syslogd(1M) mechanism.

Note –

All errors that are related to the daemon are reported by pmfd (1M). All the functions from the API return 0 on success and -1 for any failure.

The DPM Daemon monitors the availability of the logical path that is visible through multipath drivers such as Sun StorEdge Traffic Manager, HDLM, and PowerPath. The individual physical paths that are managed by these drivers are not monitored, because the multipath driver masks individual failures from the DPM daemon.

Monitoring Disk Paths

This section describes two methods for monitoring disk paths in your cluster. The first method is provided by the scdpm command. Use this command to monitor, unmonitor, or display the status of disk paths in your cluster. This command is also useful for printing the list of faulted disks and for monitoring disk paths from a file.

The second method for monitoring disk paths in your cluster is provided by the SunPlex Manager graphical user interface (GUI). SunPlex Manager provides a topological view of the monitored disk paths in your cluster. The view is updated every 10 minutes to provide information about the number of failed pings. Use the information that is provided by the SunPlex Manager GUI in conjunction with the scdpm(1M) command to administer disk paths. Refer to Chapter 10, Administering Sun Cluster With the Graphical User Interfaces, in Sun Cluster System Administration Guide for Solaris OS for information about SunPlex Manager.

Using the scdpm Command to Monitor Disk Paths

The scdpm(1M) command provides DPM administration commands that enable you to perform the following tasks:

Issue the scdpm(1M) command with the disk-path argument from any active node to perform DPM administration tasks on the cluster. The disk-path argument is always constituted of a node name and a disk name. The node name is not required and defaults to all if no node name is specified. The following table describes naming conventions for the disk path.

Note –

Use of the global disk-path name is strongly recommended, because the global disk-path name is consistent throughout the cluster. The UNIX disk-path name is not consistent throughout the cluster. The UNIX disk path for one disk can differ from cluster node to cluster node. The disk path could be c1t0d0 on one node and c2t0d0 on another node. If you use UNIX disk-path names, use the scdidadm -L command to map the UNIX disk-path name to the global disk-path name before issuing DPM commands. See the scdidadm(1M) man page.

Table 3–3 Sample Disk-Path Names

Name Type 

Sample Disk-Path Name 


Global disk path  


Disk path d1 on the schost-1 node


Disk path d1 on all nodes in the cluster


UNIX disk path  


Disk path c0t0d0s0 on the schost-1 node


All disk paths on the schost-1 node


All disk paths 


All disk paths on all nodes of the cluster 

Using SunPlex Manager to Monitor Disk Paths

SunPlex Manager enables you to perform the following basic DPM administration tasks:

Refer to the SunPlex Manager online help for procedural information about how to perform disk-path administration by using SunPlex Manager.