How to Change System Time on a Live Redundant System

[AngusETM]

Hi all,

I'm looking to find out best practice for changing the time on a live redundant system. I have two servers which are both synchronised to a time server, but for some reason this time server is 8 seconds fast.


Is there anything to avoid or watch out for when changing the time? Can this be performed without risk when the system is operational and both servers are running?

Regards,

Angus

[leoknipp]

If the time deviation is only 8 seconds changing the system time during runtime should not be a problem as some defaults e.g. the timeout for the alive watchdog for manager connections is 10 seconds.
You proably will get the information that some timestamps have be corrected if the system is receiving data with a timestamp older than the previous one.

As far as I know in a Linux system you can "slow" down the system time until the times are equal. There is no need to set the time back in one step.

Best Regards
Leopold Knipp
Senior Support Specialist

[AngusETM]

Thanks Leopold. It turns out the time server itself is ok but the servers are not synchronising often enough, so we'll need to change the WinCC OA servers rather than the time server itself.

What if the time is changed one server at a time? This would cause them to be 8 seconds apart from each other for a short period. I understand the tolerable difference is something like 30 seconds, but is there any undesirable behavior that could result?

[kilianvp]

In most projects we use "Time-Sync" https://www.speed-soft.de/software/time ... anguage=en

If you use Linux you can write a shell script to force an time snyc and add that script to cronjobs

[leoknipp]

If the time difference is below 10 seconds and the time is corrected I do not expect some problems.
Values which are received without a timestamp do get the timestamp of the active server. The passive server gets the value and timestamp send by the active server.

Best Regards
Leopold Knipp
Senior Support Specialist