3.7.0 HP StorageWorks HP Scalable NAS File Serving Software administration guide - HP Scalable NAS 3.7 for Linux (AG513-96002, October 2009)

Custom device monitor
A CUSTOM device monitor can be particularly useful when integrating HP Scalable
NAS with a custom application. Custom monitors can be configured to be either
single-active or multi-active.
You must supply the probe script for the custom monitor. In the script, probe commands
should determine the health of the device as necessary. If the device is operating
normally, the probe script should exit with exit status zero. If the device is not
operating normally, the probe script should exit with a non-zero exit status. HP
Scalable NAS will interpret the non-zero exit status as a failure of the device, and
take the appropriate action.
See Chapter 20, page 345 for information about developing probe scripts for custom
monitors and integrating monitors with custom applications.
Device monitors and failover
When you create a device monitor, you specify a list of servers on which the device
monitor will operate. The servers are placed in order: primary, backup #1, backup
#2, and so on. ClusterPulse considers the status and enablement of the servers when
determining where to activate a device monitor.
Device monitor activeness policy
ClusterPulse uses the following device monitor activeness policy to determine the
server or servers where it will make a device monitor active. The policy described
here is accurate for this release but it may change in future releases or be modified
by other HP products.
The device monitor activeness policy decision is made as follows:
1. If the device monitor on a specific server is disabled, then the device monitor
will not be made active on that server.
2. ClusterPulse considers the list of servers that are both up and enabled and that
are configured for the device monitor. Note the following:
• A server that has not finished joining the cluster (see Server access to the
SAN, page 355) is not considered up for the purpose of activating the device
monitor.
• A server is considered down if it loses coordinated communication with the
cluster (for example, the server crashed or was shut down, HP Scalable NAS
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