vSphere 7 – Virtual Watchdog Timer

By Victor Wu on 2020 年 08 月 09 日 • ( Leave a comment )

The virtual watchdog timer (vWDT) is a virtual device that detects and recovers from OS problems. This feature is introduced in vSphere 7. The device’s timeout can be initialized with VM power-on, or by the guest OS. The guest OS or an application in the guest OS can reset the device’s timeout based on a predefined logic. If the virtual WDT is not reset before its timeout, it resets or powers off the guest OS.

NOTE: This feature is based on Microsoft specifications: Watchdog Resource Table (WDRT) and Watchdog Action Table (WDAT).

The virtual WDT is useful in with high availability solutions, such as Red Hat High Availability and the MS SQL failover cluster.

The following requirements for the virtual WDT:

VM must include hardware version 17 or above.
VM must be powered off before adding the virtual WDT.
Guest OS support must be provided for the watchdog timer:
— Windows Server 2003 (WDRT)
— Windows Server 2008 onward (WDAT)
— Linux (kernel version 4.9 or above)

Virtual Watchdog Timer Specifications

The Watchdog Resource Table (WDRT) feature provides addresses of the following registers on the device along with information such as the maximum timer value, timer resolution and other vendor/device information which the guest OS can use to configure and operate the device. Typically, modern guest operating systems use the Watchdog Action Table (WDAT) integration. WDAT describes an abstract device and provides information such as the instructions that it offers (see below), minimum and maximum count value, timer resolution, some flags and other vendor/device information. The Guest OS uses this information to configure and operate the watchdog device.

WDAT instructions: