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       rrdtool create filename [--start|-b start time]
       [--step|-s step] [DS:ds-name:DST:heartbeat:min:max]


       The create function of the RRDtool lets you set up new
       Round Robin Database (RRD) files.  The file is created at
       its final, full size and filled with *UNKNOWN* data.

               The name of the RRD you want to create. RRD files
               should end with the extension .rrd. However, rrd­
               tool will accept any filename.

       --start|-b start time (default: now - 10s)
               Specifies the time in seconds since 1970-01-01 UTC
               when the first value should be added to the RRD.
               rrdtool will not accept any data timed before or
               at the time specified.

               See also AT-STYLE TIME SPECIFICATION section in
               the rrdfetch documentation for more ways to spec­
               ify time.

       --step|-s step (default: 300 seconds)
               Specifies the base interval in seconds with which
               data will be fed into the RRD.

               A single RRD can accept input from several data
               sources (DS).  (e.g. Incoming and Outgoing traffic
               on a specific communication line). With the DS
               configuration option you must define some basic
               properties of each data source you want to use to
               feed the RRD.

               ds-name is the name you will use to reference this
               particular data source from an RRD. A ds-name must
               be 1 to 19 characters long in the characters

               DST defines the Data Source Type. See the section
               on "How to Measure" below for further insight.
               The Datasource Type must be one of the following:

                   is for things like temperatures or number of
                   people in a room or value of a RedHat share.

                   is for continuous incrementing counters like
                   example, to measure the rate of people enter­
                   ing or leaving a room. Internally, derive
                   works exactly like COUNTER but without over­
                   flow checks. So if your counter does not reset
                   at 32 or 64 bit you might want to use DERIVE
                   and combine it with a MIN value of 0.

                   is for counters which get reset upon reading.
                   This is used for fast counters which tend to
                   overflow. So instead of reading them normally
                   you reset them after every read to make sure
                   you have a maximal time available before the
                   next overflow. Another usage is for things you
                   count like number of messages since the last

               heartbeat defines the maximum number of seconds
               that may pass between two updates of this data
               source before the value of the data source is
               assumed to be *UNKNOWN*.

               min and max are optional entries defining the
               expected range of the data supplied by this data
               source. If min and/or max are defined, any value
               outside the defined range will be regarded as
               *UNKNOWN*. If you do not know or care about min
               and max, set them to U for unknown. Note that min
               and max always refer to the processed values of
               the DS. For a traffic-COUNTER type DS this would
               be the max and min data-rate expected from the

               If information on minimal/maximal expected values
               is available, always set the min and/or max prop­
               erties. This will help RRDtool in doing a simple
               sanity check on the data supplied when running

               The purpose of an RRD is to store data in the
               round robin archives (RRA). An archive consists of
               a number of data values from all the defined data-
               sources (DS) and is defined with an RRA line.

               When data is entered into an RRD, it is first fit
               into time slots of the length defined with the -s
               option becoming a primary data point.

               The data is also consolidated with the consolida­
               tion function (CF) of the archive. The following
               consolidation functions are defined: AVERAGE, MIN,


       Here is an explanation by Don Baarda on the inner workings
       of rrdtool.  It may help you to sort out why all this
       *UNKNOWN* data is popping up in your databases:

       RRD gets fed samples at arbitrary times. From these it
       builds Primary Data Points (PDPs) at exact times every
       "step" interval. The PDPs are then accumulated into RRAs.

       The "heartbeat" defines the maximum acceptable interval
       between samples. If the interval between samples is less
       than "heartbeat", then an average rate is calculated and
       applied for that interval. If the interval between samples
       is longer than "heartbeat", then that entire interval is
       considered "unknown". Note that there are other things
       that can make a sample interval "unknown", such as the
       rate exceeding limits, or even an "unknown" input sample.

       The known rates during a PDP's "step" interval are used to
       calculate an average rate for that PDP. Also, if the total
       "unknown" time during the "step" interval exceeds the
       "heartbeat", the entire PDP is marked as "unknown". This
       means that a mixture of known and "unknown" sample time in
       a single PDP "step" may or may not add up to enough
       "unknown" time to exceed "heartbeat" and hence mark the
       whole PDP "unknown". So "heartbeat" is not only the maxi­
       mum acceptable interval between samples, but also the max­
       imum acceptable amount of "unknown" time per PDP (obvi­
       ously this is only significant if you have "heartbeat"
       less than "step").

       The "heartbeat" can be short (unusual) or long (typical)
       relative to the "step" interval between PDPs. A short
       "heartbeat" means you require multiple samples per PDP,
       and if you don't get them mark the PDP unknown. A long
       heartbeat can span multiple "steps", which means it is
       acceptable to have multiple PDPs calculated from a single
       sample. An extreme example of this might be a "step" of
       5mins and a "heartbeat" of one day, in which case a single
       sample every day will result in all the PDPs for that
       entire day period being set to the same average rate. --
       Don Baarda <don.baarda@baesystems.com>


       Here are a few hints on how to measure:

           Normally you have some type of meter you can read to
           get the temperature.  The temperature is not realy
           connected with a time. The only connection is that the
           temperature reading happened at a certain time. You
           can use the GAUGE data source type for this. RRRtool
           with the number of seconds in a day. Because all math
           is run with Doubles, the precision should be accept­

       It's always a Rate
           RRDtool stores rates in amount/second for COUNTER,
           DERIVE and ABSOLUTE data.  When you plot the data, you
           will get on the y axis amount/second which you might
           be tempted to convert to absolute amount volume by
           multiplying by the delta-time between the points. RRD­
           tool plots continuous data, and as such is not appro­
           priate for plotting absolute volumes as for example
           "total bytes" sent and received in a router. What you
           probably want is plot rates that you can scale to for
           example bytes/hour or plot volumes with another tool
           that draws bar-plots, where the delta-time is clear on
           the plot for each point (such that when you read the
           graph you see for example GB on the y axis, days on
           the x axis and one bar for each day).


       "rrdtool create temperature.rrd --step 300
       DS:temp:GAUGE:600:-273:5000 RRA:AVERAGE:0.5:1:1200
       RRA:MIN:0.5:12:2400 RRA:MAX:0.5:12:2400 RRA:AVER­

       This sets up an RRD called temperature.rrd which accepts
       one temperature value every 300 seconds. If no new data is
       supplied for more than 600 seconds, the temperature
       becomes *UNKNOWN*.  The minimum acceptable value is -273
       and the maximum is 5000.

       A few archives areas are also defined. The first stores
       the temperatures supplied for 100 hours (1200 * 300 sec­
       onds = 100 hours). The second RRA stores the minimum tem­
       perature recorded over every hour (12 * 300 seconds = 1
       hour), for 100 days (2400 hours). The third and the fourth
       RRA's do the same for the maximum and average temperature,


       Tobias Oetiker <oetiker@ee.ethz.ch>

1.0.45                      2002-12-20               RRDCREATE(1)

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