Applies To:
  • CitectSCADA 1.x 2.x 3.x 4.x
Summary:
I am using Citect file server redundancy with the parameter [CtEdit]Backup (now set via Computer setup Wizard, Advanced Setup, Backup Project Path). I am running Windows 95 clients with two Windows NT file servers. My project is installed on both file server, with E: mapped to the first server and F: to the second server, so my Citect INI has RUN=E:\CITECT\USER\PROJECT and BACKUP=F:\CITECT\USER\PROJECT. When I shutdown the file server, Citect will switch over to the second file server and continue to communicate correctly. However the every now and then Citect will pause for 30 seconds. After the pause Citect will run normally. What is causing this pause? 

Solution:
The pause is being caused by the time out of the Microsoft file redirector. When you shutdown the first file server, Citect will detect the failure and will swap its active project director to the second file server. This will cause a single pause in Citect as the file redirector changes over, see Q1884 for details. Once Citect has swapped its project over to the second file server all project files will be accessed from that server.

However if you are accessing other files directly then you will get a pause whenever you try to access the first file server. This can happen if you have database devices or files which are on the first server. For example using the FileOpen("E:\MYFILE.TXT") or DevOpen("MyDevice"), where MyDevice is on E: will cause the pause every time you try to open, read or write to the file. If you are using file server redundancy you should put any files on the local hard disk or in the project directory and use the [RUN] path to access. The [DATA] path is not switched on file server failure.

This is also the case for the trend files from the Citect trend server. It is recommended that the trend server save it's trend file data to it's local hard disk as it avoids this problem and gives the highest performance.

The time out and retries for the redirector have been tuned to cope with a wide variety of networks. So they tend to be far greater than is required for a high performance network. If your reduce these time out then the delays in Citect will be reduced. Your other solution is to copy your project files to the local hard disk.

CIT has confirmed this to be a problem in the Microsoft redirector. For a solution see Q1949.

 
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