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| Oracle Solaris Cluster Concepts Guide Oracle Solaris Cluster 4.1

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## Disk Path Monitoring

The current release of Oracle Solaris 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 Oracle Solaris Cluster System Administration Guide for procedural information about how to monitor, unmonitor, and check the status of disk paths.

### DPM Overview

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

The following table describes the default location for installation of DPM components.

Location | Component
--- | ---
Daemon | `/usr/cluster/lib/sc/scdpmd`
Command-line interface | `/usr/cluster/bin/cldevice`
Daemon status file (created at runtime) | `/var/run/cluster/scdpm.status`

A multi-threaded DPM daemon runs on each node. The DPM daemon (`scdpmd`) is started by an SMF service, `system/cluster/scdpm`, when a node boots. If a problem occurs, the daemon is managed by that SMF service 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. See 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 respond to 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 Oracle Solaris Cluster Event Framework and logs the new status of the path through the UNIX `syslogd` command. See the `syslogd`(1M) man page.

Note - All errors that are related to the daemon are reported by `pmfd`. 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 Oracle Solaris I/O multipathing (MPxIO), formerly named Sun StorEdge Traffic Manager, and EMC PowerPath. The individual physical paths are not monitored because the multipath driver masks individual failures from the DPM daemon.

### Monitoring Disk Paths

You can monitor disk paths in your cluster by using the `cldevice` command. Use this command to monitor, unmonitor, or display the status of disk paths in your cluster. You can also use this command to print a list of faulted disks and to monitor disk paths from a file. See the `cldevice`(1CL) man page.

#### Using the `cldevice` Command to Monitor and Administer Disk Paths

The `cldevice` command enables you to perform the following tasks:

- Monitor a new disk path

- Unmonitor a disk path

- Reread the configuration data from the CCR database

- Read the disks to monitor or unmonitor from a specified file

- Report the status of a disk path or all disk paths in the cluster

- Print all the disk paths that are accessible from a node

#### Using the `clnode set` Command to Manage Disk Path Failure

You use the `clnode set` command to enable and disable the automatic rebooting of a node when all monitored shared-disk paths fail. When you enable the `reboot_on_path_failure` property, the states of local-disk paths are not considered when determining if a node reboot is necessary. Only monitored shared disks are affected.

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