In addition to connecting to actual I/O devices, Citect SCADA supports the configuration of disk I/O devices, which exist only within your computer. The value of each variable in the disk I/O device is stored on your computer's hard disk.
Note: With the release of version 7.20, a feature called persistence could be applied to I/O devices in memory mode. Using a Persisted Memory I/O device is recommended as an alternative to using a disk I/O device, as full synchronization is supported if a server becomes unavailable for a period of time. See Persisted I/O Memory Mode for more information.
A disk I/O device is configured using the Device Communications Wizard. When specifying an I/O device type, select the Disk I/O Device option.
You are not required to configure a board of a port for a disk I/O device.
Once configured, disk I/O devices appear exactly as any other I/O device in your system, but are not connected to any field equipment. Disk I/O devices can contain any type of variable supported by Citect SCADA, and you can configure them to emulate any supported I/O device. You can also specify a generic protocol for a disk I/O device.
A disk I/O device is useful when the status of your plant needs to be restored after a planned or unplanned system shutdown. You can configure your system to continually update a disk I/O device with the subset of variables that defines the status of your plant. When you restart your system after a shutdown, Citect SCADA can restore this status immediately.
You can also use disk I/O devices for storing predefined data that needs to be recalled immediately when a process is necessary (for example, in a simple recipe system).
Note: If you create a RAM disk in the computer for the disk I/O device, you are not required to create or copy the disk file to the RAM disk. Citect SCADA automatically creates a disk file on startup. Avoid setting up your disk I/O device on a RAM disk if you want the data written to it to survive a power cycle of the servers.
If you need to edit the settings for a disk I/O device, see Disk I/O Device Setup.
See Also
Published June 2018