rrd-ds-type

    Default value: GAUGE

    The DS type is used by RRD to know how to interpret the numbers
    fetched from this datasource. There are three possibilities:

    GAUGE
        The measurement will be directly copied into the RRD
        datafile without any extra processing. Examples of this type
        of measurement include readings from thermometers, percent
        disk space free, etc.

    COUNTER

        The measurements from COUNTER datasources will be treated like
        SNMP counters. An SNMP counter increases monotonically until a
        fixed wrap-around point (usually either 2^31-2 or 2^63-2,
        depending on the size of the data type). To convert a COUNTER
        measurement into a rate (for instance, "count of octets" to
        "octets per second") RRD subtracts the previous value from the
        current one, and adjusts for any wraparound conditions. Any
        SNMP variable which is marked with the SNMP "COUNTER" data
        type would normally have its rrd-ds-type set to COUNTER, but
        unless your datasource guarantees a monotonous increase, it is
        better to use DERIVE with an rrd-min of zero.

    DERIVE 
        DERIVE is like COUNTER, but there is no overflow check, so
        negative rates are possible. This datasource type would be
        useful when you have a count of something (which may increase
        and decrease), and you want to graph the rate of change.

        With an rrd-min of zero, the DERIVE datasource type acts like
        COUNTER, except that negative samples are treated as
        unknown. Handling SNMP COUNTERs in this fashion helps reduce
        the occurrence of spikes in the graphs. Negative values can
        result from restarting the device or implementation errors in
        its SNMP agent, and are common enough to really recommend
        using DERIVE rather than COUNTER.

    ABSOLUTE 
        ABSOLUTE is for COUNTERs which get reset upon
        reading. Some SNMP variables have this property. Using
        ABSOLUTE instead of COUNTER tells RRD to compute the rate
        assuming the value is an absolute count of octets (or
        whatever) during the last polling period.

    The datasource type names are case-insensitive. They are passed
    directly through to RRD when the RRD file is created. If the
    datasource type is changed later, you must use rrd-tune to apply
    the change to the underlying RRD file. For more information about
    them, consult the RRD documentation for the create command.