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NetApp Knowledgebase

What is a Watchdog Timer?

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e-series-systems
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esg
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Applies to

  E-Series 

Answer

The watchdog is a hardware device on the controller which, when active, periodically interrupts the controller processor. The interrupt service routine in the firmware must respond with an action to placate, or reset, the watchdog hardware within a short period of time. If not placated, the watchdog device will force a hard reset (similar to sysReboot) of the entire controller hardware and firmware. Upon reset, the firmware reports that the controller had been reset by the watchdog device with the message:
WARNING: Restart by watchdog time out.

The watchdog timer is enabled for Fibre Channel because there is no equivalent of a scsi-bus-reset. The watchdog timer will reset the controller if there is no fibre channel interrupt serviced for about 5-10 seconds. The array controller generates its own interrupts to cover timers when the host is inactive.

A watchdog timer protects the system from software hangs. It provides a means for errors to be detected and resolved automatically. When the watchdog timer ticks down to 0 a system reset is triggered. The watchdog timers are present to allow an automated means of recovering in the event the software becomes hung so an administrator does not need to intervene.

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