Data Sizing and Storage in Data Historian

When estimating the amount of disk space required to run Data Historian, consider the following:

• Available disk space to install the required software components and files.

• Disk space required to store Data Historian data files.

• Disk space required to store Data Historian archive data files.

The following table describes the minimum disk space required to install the software (besides the operating system) for Data Historian.

Software	Minimum Disk Space Required
Microsoft SQL Server	See your Microsoft documentation.
Common Component Files	20 MB or more
Data Historian program files, including Workbench and documentation	3 MB

Disk Requirements for Configuration Database Files

All Data Historian configuration and event data are stored within a separate database. The configuration data in the database file remains relatively static and usually never exceeds tens of megabytes. However, if you set up events, records of event detections and results of data summaries or snapshots increase the configuration database file size as the tables fill up. Entries are also created in the log file for event-related transactions. If the database files are set to auto-size, the configuration database file expands to accommodate event-related data until the hard drive is full.

A temporary database stores tag definitions being imported from integrated HMI software.

The minimum disk space for the database files is shown in the following table.

File	Minimum Disk Space Required
Configuration database file	10 MB
Configuration log file	10 MB

By default, the configuration database is set to automatically expand at a 10% rate.

You cannot change these defaults during the installation. The databases can be resized later using Microsoft SQL Server utilities. For guidelines and more information on sizing databases, see your Microsoft SQL Server documentation.

Disk Requirements for Historical Data Files

Data Historian stores historical plant data to the hard disk in special archive files. During installation, the Data Historian is set up to log data to the following default path:

ProgramData\ICONICS\11\DataHistorian\Data

These files will be created and then filled during installation. After that, you can specify a different storage location (directory) using the Data Historian Configurator System Administration/System Settings screen. Make sure that you have allocated sufficient disk space for storing plant data for your desired length of time.

The amount of disk-based storage that will be needed depends on the number and frequency of stored tag values. The more tags, the fewer values that can be stored per tag before archiving the oldest data becomes necessary. The higher the specified tag storage rate, the faster you lose disk space.

Data Type:	Sizes:
Int8, UInt8	1 byte
Int16, UInt16	2 bytes
Int32, UInt32	4 bytes
Int64, UInt64	8 bytes
Float32	4 bytes
Float64	8 bytes
Boolean	0 bytes
String	String length x 2 bytes
Timestamp	4 bytes
Quality	1 to 3 bytes (depends on presence of sub-status code and/or history bits)

Analog and Discrete Storage Requirements

For analog and discrete tags, each value that is stored uses the storage size + 4 bytes of disk space, plus approximately 5% overhead. Use the following formula to estimate the disk usage:

Estimated disk usage per day = (Storage Size + Timestamp + Quality + 1) × (1 + Reserve Percentage ÷ 100) × Number of Tags × Approximate Samples per Day

Example: The estimated daily disk usage for 10,000 Float32 analog tags, where the storage size is 4 bytes and values are collected every 10 seconds. This sampling rate results in 8,640 samples per day per tag (6 samples per minute × 60 minutes × 24 hours).

(4 + 4 + 1 + 1) × (1 + 5 ÷ 100) × 10,000 × 8,640 = approximately 907 MB per day.

To achieve the best write/read performance, data slot sizes should be a multiple of disk allocation units. Data slot sizes are configurable in whole kilobytes between 1 and 255; the default value is 4 KB. Each data tag has an allocated standalone data slot.

To be precise in your calculations, you should consider the size of a single data slot. Count the number of values in (single slot + reserve for future updates), then multiply it by the number of data slots.

Example: The data slot size is 4 KB by default, and there are 10,000 tags. The initial update of each tag creates a file with a size of (10,000 × 4 KB) + 4 KB for the header, or approximately 40 MB. This size remains unchanged until the data slots are full; then it creates more data slots as needed.

String Storage Requirements

For strings, the number of bytes required for storage will be the actual number of characters being sent from the data source + 14 bytes, plus 15% overhead. Therefore, the average disk usage per day for a variable-length string that is receiving an average of 'N' characters per sample could be calculated using the following formula:

Estimated average disk usage per day is (1.15 × (N + 14) x number of tags) × (60 ÷ average storage rate in seconds) x 60 minutes × 24 hours ÷ NTFS compression ratio.

Example: The disk usage for 10,000 60-byte string tags that are changing, on average, every 60 seconds, with the average length of an incoming value 60 characters:

(1.15 × (60 + 14) × 5,000) × (60 ÷ 60) × 60 x 24 ÷ 2 = approximately 292 MB per day