Running Reliance SCADA on an SSD

March 21, 2016

Using SSD hard drives (solid-state drives) has recently become very popular not only in industrial automation. Compared to platter disks (HDD), solid-state drives have the following advantages:

High read and write speed
No mechanical components (they are resistant to shock, vibration, etc.)
Low operating temperature
Small in size

On the other hand, the following drawbacks prevent them from large-scale use:

High price per unit of storage
Shorter drive lifetime (from the point of view of the number of drive writes)
Shorter data lifetime (from a long-term point of view)
Shorter data lifetime in environments with higher temperatures

The fact that the number of drive writes affects the lifetime of SSDs can cause a problem when using SCADA systems as these are generally used for collecting, storing, and, subsequently, presenting data. Therefore, you should consider in advance whether it is suitable to run SCADA systems or even store data on an SSD. Exceeding the number of rewrites guaranteed by the manufacturer may cause irreversible damage to data and its loss with no possibility to complain.

Solid-state drive (Source: Flickr, Author, CC BY 2.0)

What data is stored on disk by Reliance SCADA?

The following data is stored on disk by the Reliance SCADA system:

Historical tag values (data tables)
Alarms/events
Postmort records
Last (current) tag values
Real-time trend history
Recipes
Web server statistics
User profiles
Window records
Component data
Files in project-defined scripts
Log files of the main modules and communication drivers

To make the lifetime of SSDs longer, the number of writes must be minimized. Some of the above data can be influenced by the settings (storage device, logging interval, etc.), other data is logged to the visualization project directory. However, data logging can be disabled (suppressed). Below are two typical situations and the respective recommendations.

1. The computer only has an SSD

It is therefore important to realize that only a storage device with a limited number of drive writes is available, so you should configure the project settings to minimize the number of write operations.

1.1 Historical data, alarms/events

This data can be stored in an SQL-based database. If there is a computer equipped with an SQL server within the network, we recommend this server as a data storage destination. If for any reason you need to use a file-based database (dBASE), we recommend that you consider storing the data in a network drive. If the data cannot be stored on another computer, it is necessary to try to minimize the number of writes by extending the historical data logging interval (the sampling interval may be configured as needed).

1.2 Postmort, recipes, user profiles, window records

For this type of data, you can choose a storage device. Particularly in case of Postmort records, you should consider changing the storage device to a network drive.

1.3 Log files

We recommend that you disable logging for the main modules and communication drivers. As a last resort, you can choose a network drive for storing the log files. However, this is not recommended because of the fact that the amount of logging information is unpredictable.

1.4 Writing data to files from scripts

This is, for example, report generation to PDF or data logging to a CSV file. You should attempt to minimize the amount of these operations or to write data to a network drive.

1.5 Web server statistics

If your computer is not a server for thin clients, custom applications, or Reliance OPC Server, we recommend that you turn off the Web server.

1.6 Real-time trend history, last (current) tag values, component data

In this case, data logging cannot be disabled or configured. If you need help on this, please contact the Reliance technical support team.

Tips for running the Reliance SCADA system on an SSD

For online monitoring of disk writes, you can use the Process Monitor tool (free).
To determine the lifetime of an SSD, you can use the SSD Life program (shareware).
It is generally recommended to use SSDs for Windows 7 or newer operating systems because they support TRIM. Additionally, it is advised to check whether TRIM is enabled in Windows (see this article).

2. The computer has both an SSD and an HDD

In this case, we definitely recommend that you store your visualization project on an HDD. Further, we advise that you check whether or not a path for storing data on an SSD is defined in the project settings.

Improved support for SSDs in Reliance 4.7.2

In Reliance 4.7.2, we have improved the way some files are stored on disk. Now, the number of writes is minimized. We have also added detecting an SSD at project startup. If the computer only has an SSD and logging for the main modules and communication drivers is enabled, a warning message is displayed.