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  1. #1
    Join Date
    Feb 2008
    Purcellville Va.
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    Calculating trend usage in EC-BOS-8

    Any help is greatly appreciated.

    I am wanting to calculate approximate data usage for trending in a Distech EC-Bos-8.

    I know what points I want to trend and the frequency and therefor the number of entries per day.

    How would I figure the the number of bit/bytes per history?

    The data points are mostly AI's and BI's from AAON VCCx2 controllers.


  2. #2
    Join Date
    Apr 2007
    San Diego, CA
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    I had this document saved from a while back, it has some of my notes merged with notes from James @ Niagara-Community.

    These maximum file handle limits have changed over time, below are the current limits for the number of active file handles and the maximum number of recommended histories.

    AX 3.8
    JACE Model		FD Limit	History Limit
    JACE 2			1000		800
    JACE 3/4/5		2000		1600
    JACE 6/6E/603/645	2000		1600
    JACE 7			3000		2400
    JACE Model		FD Limit	History Limit
    JACE 3			2000		1600
    JACE 6/6E/603/645	2000		1600
    JACE 7			3000		2400
    JACE 8000	        8000	        6000
    To calculate the potential capacity setting of histories you need to consider the quantity of each type of history, the available RAM disk space, and the available flash drive space.

    In Niagara AX, history files have a header which is ~1600 bytes to store configuration information and uses page files which are 4096 bytes to store the records. The standard control point type histories have very predictable sizes.

    Boolean = 13 bytes/record
    Enum and Single Precision Numeric = 16 bytes/record
    Double Precision Numeric = 20 bytes/record
    String = variable size depending on characters and cannot span page files, max 4096 bytes/record

    String type history records are variable in size and are dependent upon the number of characters being stored in a record. Generally speaking if using English language each character represents a single byte, while if using non-English languages many characters require multiple bytes. This applies to things like the audit history, log history, String COV or interval history, and the alarm database.

    You do need to maintain sufficient free space on both the RAM disk and flash drive to allow saving working copies of the files for saving the history database, alarm database and station.

    The number of records is dependent on the number of histories being collected and the available space on the RAM disk and the flash drive. During run-time the history and alarm database files are stored on the RAM disk. During station save the history and alarm database files are zipped and saved to the flash drive.

    In Niagara4 the encoding has changed for timestamps and statuses in histories, which slightly reduce the record size compared to AX.
    Boolean - 9 bytes/record
    Numeric single precision or Enum - 12 bytes/record
    Numeric double precision - 16 bytes/record
    String - varies, but generally 1 byte/English character, and can be multiple bytes/character for Unicode or other language.

    You should be able to do the math to figure out how much flash drive and RAM disk space will be required for your histories.

    As an example, a single precision numeric history, collecting at a 15 minute interval and retained for one month:

    4 records/hr * 24 hrs/day * 30 days/year = 2880 records. * 12 bytes/rec = 34,560 bytes (34.56KB)

    For 6000 histories collected at a 15 minute interval maintaining 1 month worth of data would be 6,000 * 34.56KB = 207,360KB or 207.36MB

    This is a rough calculation, but should get you pretty close. Understand that the log history, audit history and alarm database files also exist on both the flash drive and RAM disk as well.
    Last edited by digo; 11-07-2018 at 07:32 PM. Reason: table formatting

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