Disk space estimation

This section provides guidance on how to determine the appropriate history block duration. A history block duration can range from 1 hour to 24 hours, with a default of 24 hours.

For retrieval performance, it is better to have longer block durations. However, if the incoming data rate is too high during a 24-hour period, the Original.dat file in which data collects may grow so large that issues occur for history block management and other aspects of the storage subsystem.

We recommend that you tune the history block duration so that the size of the Original.dat file does not exceed 8 GB per history block.

You can estimate how many bytes this data rate generates in one hour by using the following formula:

N kbps = (N / 8) bytes per second = (450 * N) bytes per hour

Where N is the transmission item size for the type of data that you are storing. For information on calculating this number, see Storage and network transmission sizes for tags.

If you multiply this by the history block duration, you can get an estimate of the biggest data file containing streamed and forwarded data, Original.dat.

If that estimate is larger than 8 GB, keep reducing the history block duration until the estimate is under the 8 GB limit.