Manual Redundancy Switchover (Usurping)

To choose the peer driver (I/O server) on which a unit will be active, use the following tags:

Primary request tags:

• Unit<n>.RequestUnitActive.Primary

Writing 1 to a primary request tag causes the unit to be active on the driver on the primary I/O server. Writing 0 causes the unit to be active on the driver on the standby I/O server.

Standby request tags:

• Unit<n>.RequestUnitActive.Standby

Writing 1 to a standby request tag causes the unit to be active on the driver on the standby I/O server. Writing 0 causes the unit to be active on the driver on the primary I/O server.

The request tags can be read at any time, and return the value last written to the tag.

The user can monitor which peer driver (I/O server) has an active unit, using the following tags:

• Unit<n>.UnitActiveState.Primary

• Unit<n>.UnitActiveState.Standby

If the unit is active on the primary I/O server driver, then the primary tags return 1 and the standby tags return 0. If the unit is active on the standby I/O server driver, then the standby tags return 1 and the primary tags return 0.

You can also use the following addresses to determine a port's online status for diagnostic purposes.

• Unit<n>.UnitPortState.Primary

• Unit<n>.UnitPortState.Standby

This online status is the TRUE online status. Be aware of this when using ExclusiveAccess mode for ports. Remember that the port that is reported on is the one which matches your tag. If required, you can have units on one port that are PRIMARY, STANDBY, PRIMARY, and so on.