Applies To:
  • CitectSCADA 3.xx, 4.xx, 5.xx

I have followed the online help but I am still having trouble configuring a redundant disk plc. Can you please give me an example of how to configure this? 

To configure a redundant disk device set up the following records in your project.

IO Server:

IO Devices:

Server Name:  IOSERVER1
Number: 1
Address: C:\Primary.cdk,X:\Standby.cdk
Protocol: GENERIC
Port Name: DISKDRV
Startup Mode: Primary (enable Extended Forms to see this field)


Server Name:  IOSERVER2
Number: 1
Address: C:\Standby.cdk,X:\Primary.cdk
Protocol: GENERIC
Port Name: DISKDRV
Startup Mode: StandbyWrite

Note: do not leave a space after the comma and before the other units drive letter in the Address fields.


  1. Use the Computer Setup Wizard to Configure two PCs as IOServers. ie IOSERVER1 and IOSERVER2.
  2. Map the C drive of the remote PC to the local drive letter X (NB must first have the C drives shared - use Windows Explorer to do this)
  3. Run the projects and confirm that the files: Primary.cdk and Standby.cdk get created on IOSERVER1 and IOSERVER2 respectively.
  4. To test: Configure a digital test tag, shutdown the primary IOServer IOSERVER1, and toggle the bit on IOSERVER2. Restart IOSERVER1 and check that the value has been updated.


  • It is critical that both IODevices have the same number.
  • You can use path substitution in the IODevice address field, for the primary file only. ie substitute C:\Primary.cdk in the first record and X:\Primary.cdk in the second record. Note that this path substitution restriction has been lifted in recent Citect versions.
  • Ensure the Date, Time and Daylight Savings regional settings in the Windows Control Panel are the same on both PCs. Otherwise, the timestamp on the disk files will be inconsistent and the older file may be copied over the newer file at startup (resulting in the loss of the latest changes to disk device variables).