Disk space requirements for historical data files

The Historian stores historical plant data to hard disk in special files called history blocks. When you install the Historian, you are required to specify a storage location (directory) in which these files will be dynamically created and subsequently filled. You must have at least 200 MB of free disk space for these files to install the Historian.

After the Historian is up and running, when the free space on the drive containing the storage directory drops below a minimum threshold, the oldest data is overwritten. It is very important that you allocate enough disk space to store your plant data for the desired length of time.

The amount of data that can be stored to disk before running out of space is dependent upon the number of tag values that are stored and how often they are stored. That is, the more tags you have, the fewer values you can store per tag before you need to archive off the oldest data. Likewise, the higher the specified storage rate per tag, the faster the system runs out of space.

Important: You must have sufficient disk space in the circular storage area to hold at least two full history blocks, plus the space specified for the minimum threshold for the circular storage area. Use the Operations Control Management Console to view or change the minimum threshold value.

A performance report for different historian systems is provided in System sizing examples.