Enterprise Historian Disk Space Requirements
This forumula can be used to estimate the daily storage requirements:Disk Space Required = Total Updates * Change Rate * Average bytes per TVQ
Total Updates
number of tags * updates per day
(A one second log rate will generate 86,400 updates / day)
Change Rate
is how often the data value changes between successive readings.
(Normally this is 40 to 80% for analog values and 5 to 20% for discrete values.)
A TVQ is a storage unit of a Timestamp, Value and Quality. The timestamp is accurate to 100ns, the value is a variant and the quality is 16 bit OPC quality.
| Data Type | Average Bytes per TVQ |
| Bool | 3 |
| I2 (2 byte Integer) | 4 |
| R4 (4 byte Real) | 6 |
| I4 | 6 |
| R8 | 10 |
Example: A system logging 500 analog tags (4 byte floating point values) at a 2 second interval with an average change rate of 50% will require approximately 62 Mb/day.
Compute Your Disk Space Requirements with Excel