Applies To:
  • CitectSCADA  All versions up to 7.0

I have a new hard disk capable of high-speed writes, yet CitectSCADA does not seem to take advantage of this when creating Trend History Files on start-up. Why is that?  

CitectSCADA 7.0, by default, will limit the number of bytes written per write request to 16,384 bytes before sleeping. This is controlled by the [Trend] BytesWrittenBeforeSleep citect.ini parameter. The help file suggests that this parameter can be set to a maximum of 1,000,000 bytes, which is true but only for writing to the trend files at runtime . On start-up this parameter will only make a difference up to 32,768 bytes. Any value above that, will be capped to 32,768 bytes by CitectSCADA.

This is however only one of a number of factors that may affect the performance of Trend History File creation at start-up. Keep in mind that having a trend system which has a large number of history files with small file sizes may experience lower write speeds as there is added overhead for the creation of each file.

It is good practice to minimise the amount of trend data that you're storing with CitectSCADA. You should focus on trending values that are important to end users rather than trying to trend each variable tag in your project. Also, you should avoid trying to store multiple years worth of trend data, especially if you have a large number of trends. If you require such functionality then we recommend that look at using the Historian component of CitectSCADA Reports.