DPM Overview

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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.

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.
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.
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.
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.