Uninstalling a driver with minimum outage

murrayclay · ‎2022-06-21

Hi All,

Can anyone offer some advice / have experience with removing a redundant driver from a hot standby pair?

We are planning to remove a driver (PDSSymax) from a server cluster that consists of two servers in Main-Hot Standby relationship and two Permanent Standby Servers. Due to the size of the database these servers can take a while to shutdown and start again. As such we are attempting to devise a strategy that will not lose any DNP3 history and have the shortest possible outage for the SCADA end users. We are aware that a standby server can have more drivers installed than the main server and still be able to synchronize with the main. However, a main server that has more drivers installed than the standby server(s) will not be able to synchronize with those server(s).

We have investigated if Duty Mode can be used to minimise the outage as it is currently enabled between the Main-Standby pair. We are aware that this mode is intended to retain history from both servers in a Main-Main situation, but have also found that it can be used to combine history between the two servers if they were to each contain history the other did not (i.e. without main-main situation). We have tested this in a development environment without the Permanent Standbys and it appears to work with the following steps.

Both server synchronised
Server B Shutdown
Driver Removed from Server B
History added to running Server A
Server A shutdown
Both servers off
Server B started as Main
Driver Removed from Server A
History added to running Server B
Server A started
Both servers synchronised

At step 11 the data from step 4 and step 9 are both present.

Hoping to get peoples feedback on the above process and also whether people have other ideas or experience with minimising outage while uninstalling a driver.

Thanks in advance.