Citect SCADA uses blocking file opens which means that saving data on network fileservers could be blocked for the duration of the open. Normal network and fileserver performance is such that the duration of the blocking step is below the threshold of detection for human interaction. But in the case of an outage of one of the components, SCADA operators could observe periods of no response from SCADA for up to 40 seconds approximately.

For example, 10 seconds is about the length of the time it takes for Windows file open to fail name resolution component of file open on some systems. If name resolution is successful, but the IP address is not reachable, the time taken is more like an average of 30 seconds. If the IP address was contactable, but the target machine is in a severely degraded state, this could take longer still, but the typical situations are name resolution issues or fileserver availability issues. These typical situations may be in turn be caused by either a network issue such as a failed link, failed network component, or a soft failure such as packet loss, or the issue could be with the host computers involved such as the DNS machine or the target fileserver machine not being available.

Internal testing of duration for file opens using invalid server names is either 9 or 11.3 seconds. That is the observations a bi-modal with very little variation. Hence the term average can be somewhat misleading. Similar testing using invalid IP addresses gives times of either 21 or 42 seconds. Again, bi-modal so the use of an average of 30 seconds can also mislead. These results were taken on a standard Intel 32 machine running Windows XP SP2.