rrdcreate(1) 맨 페이지 - 윈디하나의 솔라나라




     rrdcreate - Set up a new Round Robin Database

     rrdtool create filename [--start|-b start time]
     [--step|-s step] [--template|-t template-file]
     [--source|-r source-file] [--no-overwrite|-O]
     [--daemon|-d address] [DS:ds-name[=mapped-ds-name[[source-
     index]]]:DST:dst arguments] [RRA:CF:cf arguments]

     The create function of 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, unless one
     or more source RRD files have been specified and they hold
     suitable data to "pre-fill" the new RRD file.

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

  --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 other ways to specify time.

     If one or more source files is used to pre-fill the new RRD,
     the --start option may be omitted. In that case, the latest
     update time among all source files will be used as the last
     update time of the new RRD file, effectively setting the
     start time.

  --step|-s step (default: 300 seconds)
     Specifies the base interval in seconds with which data will
     be fed into the RRD.  A scaling factor may be present as a
     suffix to the integer; see "STEP, HEARTBEAT, and Rows As

     Do not clobber an existing file of the same name.

  --daemon|-d address
     Address of the rrdcached daemon.  For a list of accepted
     formats, see the -l option in the rrdcached manual.

      rrdtool create --daemon unix:/var/run/rrdcached.sock /var/lib/rrd/foo.rrd I<other options>

  [--template|-t template-file]
     Specifies a template RRD file to take step, DS and RRA
     definitions from. This allows one to base the structure of a
     new file on some existing file. The data of the template
     file is NOT used for pre-filling, but it is possible to
     specify the same file as a source file (see below).

     Additional DS and RRA definitions are permitted, and will be
     added to those taken from the template.

  --source|-r source-file
     One or more source RRD files may be named on the command
     line. Data from these source files will be used to prefill
     the created RRD file. The output file and one source file
     may refer to the same file name. This will effectively
     replace the source file with the new RRD file. While there
     is the danger to loose the source file because it gets
     replaced, there is no danger that the source and the new
     file may be "garbled" together at any point in time, because
     the new file will always be created as a temporary file
     first and will only be moved to its final destination once
     it has been written in its entirety.

     Prefilling is done by matching up DS names, RRAs and
     consolidation functions and choosing the best available data
     resolution when doing so. Prefilling may not be
     mathematically correct in all cases (eg. if resolutions have
     to change due to changed stepping of the target RRD and old
     and new resolutions do not match up with old/new bin
     boundaries in RRAs).

     In other words: A best effort is made to preserve data
     during prefilling.  Also, pre-filling of RRAs may only be
     possible for certain kinds of DS types. Prefilling may also
     have strange effects on Holt-Winters forecasting RRAs. In
     other words: there is no guarantee for data-correctness.

     When "pre-filling" a RRD file, the structure of the new file
     must be specified as usual using DS and RRA specifications
     as outlined below. Data will be taken from source files
     based on DS names and types and in the order the source
     files are specified in. Data sources with the same name from
     different source files will be combined to form a new data
     source. Generally, for any point in time the new RRD file
     will cover after its creation, data from only one source
     file will have been used for pre-filling. However, data from
     multiple sources may be combined if it refers to different
     times or an earlier named source file holds unknown data for
     a time where a later one holds known data.

     If this automatic data selection is not desired, the DS
     syntax allows one to specify a mapping of target and source
     data sources for prefilling. This syntax allows one to
     rename data sources and to restrict prefilling for a DS to
     only use data from a single source file.

     Prefilling currently only works reliably for RRAs using one
     of the classic consolidation functions, that is one of:
     AVERAGE, MIN, MAX, LAST. It might also currently have
     problems with COMPUTE data sources.

     Note that the act of prefilling during create is similar to
     a lot of the operations available via the tune command, but
     using create syntax.

  DS:ds-name[=mapped-ds-name[[source-index]]]:DST:dst arguments
     A single RRD can accept input from several data sources
     (DS), for example 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 store in 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 [a-zA-Z0-9_].

     DST defines the Data Source Type. The remaining arguments of
     a data source entry depend on the data source type. For
     format for a data source entry is:


     For COMPUTE data sources, the format is:


     In order to decide which data source type to use, review the
     definitions that follow. Also consult the section on "HOW TO
     MEASURE" for further insight.

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

         is for continuous incrementing counters like the
         ifInOctets counter in a router. The COUNTER data source
         assumes that the counter never decreases, except when a
         counter overflows.  The update function takes the
         overflow into account.  The counter is stored as a per-
         second rate. When the counter overflows, RRDtool checks
         if the overflow happened at the 32bit or 64bit border
         and acts accordingly by adding an appropriate value to
         the result.

         the same as COUNTER, but for quantities expressed as
         double-precision floating point number.  Could be used
         to track quantities that increment by non-integer
         numbers, i.e. number of seconds that some routine has
         taken to run, total weight processed by some technology
         equipment etc.  The only substantial difference is that
         DCOUNTER can either be upward counting or downward
         counting, but not both at the same time.  The current
         direction is detected automatically on the second non-
         undefined counter update and any further change in the
         direction is considered a reset.  The new direction is
         determined and locked in by the second update after
         reset and its difference to the value at reset.

         will store the derivative of the line going from the
         last to the current value of the data source. This can
         be useful for gauges, for example, to measure the rate
         of people entering or leaving a room. Internally, derive
         works exactly like COUNTER but without overflow 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.

         the same as DERIVE, but for quantities expressed as
         double-precision floating point number.

         NOTE on COUNTER vs DERIVE

         by Don Baarda <don.baarda@baesystems.com>

         If you cannot tolerate ever mistaking the occasional
         counter reset for a legitimate counter wrap, and would
         prefer "Unknowns" for all legitimate counter wraps and
         resets, always use DERIVE with min=0. Otherwise, using
         COUNTER with a suitable max will return correct values
         for all legitimate counter wraps, mark some counter
         resets as "Unknown", but can mistake some counter resets
         for a legitimate counter wrap.

         For a 5 minute step and 32-bit counter, the probability
         of mistaking a counter reset for a legitimate wrap is
         arguably about 0.8% per 1Mbps of maximum bandwidth. Note
         that this equates to 80% for 100Mbps interfaces, so for
         high bandwidth interfaces and a 32bit counter, DERIVE
         with min=0 is probably preferable. If you are using a
         64bit counter, just about any max setting will eliminate
         the possibility of mistaking a reset for a counter wrap.

         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 maximum time
         available before the next overflow. Another usage is for
         things you count like number of messages since the last

         is for storing the result of a formula applied to other
         data sources in the RRD. This data source is not
         supplied a value on update, but rather its Primary Data
         Points (PDPs) are computed from the PDPs of the data
         sources according to the rpn-expression that defines the
         formula. Consolidation functions are then applied
         normally to the PDPs of the COMPUTE data source (that is
         the rpn-expression is only applied to generate PDPs). In
         database software, such data sets are referred to as
         "virtual" or "computed" columns.

     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 define the expected range values for data
     supplied by a data source. If min and/or max are specified
     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 maximum and minimum data-rate expected
     from the device.

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

     rpn-expression defines the formula used to compute the PDPs
     of a COMPUTE data source from other data sources in the same
     <RRD>. It is similar to defining a CDEF argument for the
     graph command. Please refer to that manual page for a list
     and description of RPN operations supported. For COMPUTE
     data sources, the following RPN operations are not
     supported: COUNT, PREV, TIME, and LTIME. In addition, in
     defining the RPN expression, the COMPUTE data source may
     only refer to the names of data source listed previously in
     the create command. This is similar to the restriction that
     CDEFs must refer only to DEFs and CDEFs previously defined
     in the same graph command.

     When pre-filling the new RRD file using one or more source
     RRDs, the DS specification may hold an optional mapping
     after the DS name. This takes the form of an equal sign
     followed by a mapped-to DS name and an optional source index
     enclosed in square brackets.

     For example, the DS


     specifies that the DS named a should be pre-filled from the
     DS named b in the second listed source file (source indices
     are 1-based).

  RRA:CF:cf arguments
     The purpose of an RRD is to store data in the round robin
     archives (RRA). An archive consists of a number of data
     values or statistics for each of 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, thus
     becoming a primary data point.

     The data is also processed with the consolidation function
     (CF) of the archive. There are several consolidation
     functions that consolidate primary data points via an
     aggregate function: AVERAGE, MIN, MAX, LAST.

         the average of the data points is stored.

     MIN the smallest of the data points is stored.

     MAX the largest of the data points is stored.

         the last data points is used.

     Note that data aggregation inevitably leads to loss of
     precision and information. The trick is to pick the
     aggregate function such that the interesting properties of
     your data is kept across the aggregation process.

     The format of RRA line for these consolidation functions is:

     RRA:{AVERAGE | MIN | MAX | LAST}:xff:steps:rows

     xff The xfiles factor defines what part of a consolidation
     interval may be made up from *UNKNOWN* data while the
     consolidated value is still regarded as known. It is given
     as the ratio of allowed *UNKNOWN* PDPs to the number of PDPs
     in the interval. Thus, it ranges from 0 to 1 (exclusive).

     steps defines how many of these primary data points are used
     to build a consolidated data point which then goes into the
     archive.  See also "STEP, HEARTBEAT, and Rows As Durations".

     rows defines how many generations of data values are kept in
     an RRA.  Obviously, this has to be greater than zero.  See
     also "STEP, HEARTBEAT, and Rows As Durations".

Aberrant Behavior Detection with Holt-Winters Forecasting
     In addition to the aggregate functions, there are a set of
     specialized functions that enable RRDtool to provide data
     smoothing (via the Holt-Winters forecasting algorithm),
     confidence bands, and the flagging aberrant behavior in the
     data source time series:

     *   RRA:HWPREDICT:rows:alpha:beta:seasonal period[:rra-num]

     *   RRA:MHWPREDICT:rows:alpha:beta:seasonal period[:rra-num]

     *   RRA:SEASONAL:seasonal period:gamma:rra-

     *   RRA:DEVSEASONAL:seasonal period:gamma:rra-

     *   RRA:DEVPREDICT:rows:rra-num

     *   RRA:FAILURES:rows:threshold:window length:rra-num

     These RRAs differ from the true consolidation functions in
     several ways.  First, each of the RRAs is updated once for
     every primary data point.  Second, these RRAs are
     interdependent. To generate real-time confidence bounds, a
     matched set of SEASONAL, DEVSEASONAL, DEVPREDICT, and either
     HWPREDICT or MHWPREDICT must exist. Generating smoothed
     values of the primary data points requires a SEASONAL RRA
     and either an HWPREDICT or MHWPREDICT RRA. Aberrant behavior
     detection requires FAILURES, DEVSEASONAL, SEASONAL, and

     The predicted, or smoothed, values are stored in the
     actually two variations on the Holt-Winters method. They are
     interchangeable. Both attempt to decompose data into three
     components: a baseline, a trend, and a seasonal coefficient.
     HWPREDICT adds its seasonal coefficient to the baseline to
     form a prediction, whereas MHWPREDICT multiplies its
     seasonal coefficient by the baseline to form a prediction.

     The difference is noticeable when the baseline changes
     significantly in the course of a season; HWPREDICT will
     predict the seasonality to stay constant as the baseline
     changes, but MHWPREDICT will predict the seasonality to grow
     or shrink in proportion to the baseline. The proper choice
     of method depends on the thing being modeled. For
     simplicity, the rest of this discussion will refer to
     HWPREDICT, but MHWPREDICT may be substituted in its place.

     The predicted deviations are stored in DEVPREDICT (think a
     standard deviation which can be scaled to yield a confidence
     band). The FAILURES RRA stores binary indicators. A 1 marks
     the indexed observation as failure; that is, the number of
     confidence bounds violations in the preceding window of
     observations met or exceeded a specified threshold. An
     example of using these RRAs to graph confidence bounds and
     failures appears in rrdgraph.

     The SEASONAL and DEVSEASONAL RRAs store the seasonal
     coefficients for the Holt-Winters forecasting algorithm and
     the seasonal deviations, respectively.  There is one entry
     per observation time point in the seasonal cycle. For
     example, if primary data points are generated every five
     minutes and the seasonal cycle is 1 day, both SEASONAL and
     DEVSEASONAL will have 288 rows.

     In order to simplify the creation for the novice user, in
     addition to supporting explicit creation of the HWPREDICT,
     RRDtool create command supports implicit creation of the
     other four when HWPREDICT is specified alone and the final
     argument rra-num is omitted.

     rows specifies the length of the RRA prior to wrap around.
     Remember that there is a one-to-one correspondence between
     primary data points and entries in these RRAs. For the
     HWPREDICT CF, rows should be larger than the seasonal
     period. If the DEVPREDICT RRA is implicitly created, the
     default number of rows is the same as the HWPREDICT rows
     argument. If the FAILURES RRA is implicitly created, rows
     will be set to the seasonal period argument of the HWPREDICT
     RRA. Of course, the RRDtool resize command is available if
     these defaults are not sufficient and the creator wishes to
     avoid explicit creations of the other specialized function

     seasonal period specifies the number of primary data points
     in a seasonal cycle. If SEASONAL and DEVSEASONAL are
     implicitly created, this argument for those RRAs is set
     automatically to the value specified by HWPREDICT. If they
     are explicitly created, the creator should verify that all
     three seasonal period arguments agree.
     alpha is the adaption parameter of the intercept (or
     baseline) coefficient in the Holt-Winters forecasting
     algorithm. See rrdtool for a description of this algorithm.
     alpha must lie between 0 and 1. A value closer to 1 means
     that more recent observations carry greater weight in
     predicting the baseline component of the forecast. A value
     closer to 0 means that past history carries greater weight
     in predicting the baseline component.

     beta is the adaption parameter of the slope (or linear
     trend) coefficient in the Holt-Winters forecasting
     algorithm. beta must lie between 0 and 1 and plays the same
     role as alpha with respect to the predicted linear trend.

     gamma is the adaption parameter of the seasonal coefficients
     in the Holt-Winters forecasting algorithm (HWPREDICT) or the
     adaption parameter in the exponential smoothing update of
     the seasonal deviations. It must lie between 0 and 1. If the
     SEASONAL and DEVSEASONAL RRAs are created implicitly, they
     will both have the same value for gamma: the value specified
     for the HWPREDICT alpha argument. Note that because there is
     one seasonal coefficient (or deviation) for each time point
     during the seasonal cycle, the adaptation rate is much
     slower than the baseline. Each seasonal coefficient is only
     updated (or adapts) when the observed value occurs at the
     offset in the seasonal cycle corresponding to that

     If SEASONAL and DEVSEASONAL RRAs are created explicitly,
     gamma need not be the same for both. Note that gamma can
     also be changed via the RRDtool tune command.

     smoothing-window specifies the fraction of a season that
     should be averaged around each point. By default, the value
     of smoothing-window is 0.05, which means each value in
     SEASONAL and DEVSEASONAL will be occasionally replaced by
     averaging it with its (seasonal period*0.05) nearest
     neighbors.  Setting smoothing-window to zero will disable
     the running-average smoother altogether.

     rra-num provides the links between related RRAs. If
     HWPREDICT is specified alone and the other RRAs are created
     implicitly, then there is no need to worry about this
     argument. If RRAs are created explicitly, then carefully pay
     attention to this argument. For each RRA which includes this
     argument, there is a dependency between that RRA and another
     RRA. The rra-num argument is the 1-based index in the order
     of RRA creation (that is, the order they appear in the
     create command). The dependent RRA for each RRA requiring
     the rra-num argument is listed here:

     *   HWPREDICT rra-num is the index of the SEASONAL RRA.
     *   SEASONAL rra-num is the index of the HWPREDICT RRA.

     *   DEVPREDICT rra-num is the index of the DEVSEASONAL RRA.

     *   DEVSEASONAL rra-num is the index of the HWPREDICT RRA.

     *   FAILURES rra-num is the index of the DEVSEASONAL RRA.

     threshold is the minimum number of violations (observed
     values outside the confidence bounds) within a window that
     constitutes a failure. If the FAILURES RRA is implicitly
     created, the default value is 7.

     window length is the number of time points in the window.
     Specify an integer greater than or equal to the threshold
     and less than or equal to 28.  The time interval this window
     represents depends on the interval between primary data
     points. If the FAILURES RRA is implicitly created, the
     default value is 9.

STEP, HEARTBEAT, and Rows As Durations
     Traditionally RRDtool specified PDP intervals in seconds,
     and most other values as either seconds or PDP counts.  This
     made the specification for databases rather opaque; for

      rrdtool create power.rrd \
        --start now-2h --step 1 \
        DS:watts:GAUGE:300:0:24000 \
        RRA:AVERAGE:0.5:1:864000 \
        RRA:AVERAGE:0.5:60:129600 \
        RRA:AVERAGE:0.5:3600:13392 \

     creates a database of power values collected once per
     second, with a five minute (300 second) heartbeat, and four
     RRAs: ten days of one second, 90 days of one minute, 18
     months of one hour, and ten years of one day averages.

     Step, heartbeat, and PDP counts and rows may also be
     specified as durations, which are positive integers with a
     single-character suffix that specifies a scaling factor.
     See "rrd_scaled_duration" in librrd for scale factors of the
     supported suffixes: "s" (seconds), "m" (minutes), "h"
     (hours), "d" (days), "w" (weeks), "M" (months), and "y"

     Scaled step and heartbeat values (which are natively
     durations in seconds) are used directly, while consolidation
     function row arguments are divided by their step to produce
     the number of rows.

     With this feature the same specification as above can be
     written as:

      rrdtool create power.rrd \
        --start now-2h --step 1s \
        DS:watts:GAUGE:5m:0:24000 \
        RRA:AVERAGE:0.5:1s:10d \
        RRA:AVERAGE:0.5:1m:90d \
        RRA:AVERAGE:0.5:1h:18M \

     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:

     RRDtool gets fed samples/updates at arbitrary times. From
     these it builds Primary Data Points (PDPs) on every "step"
     interval. The PDPs are then accumulated into the RRAs.

     The "heartbeat" defines the maximum acceptable interval
     between samples/updates. 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 a sample that was explicitly
     marked as unknown.

     The known rates during a PDP's "step" interval are used to
     calculate an average rate for that PDP. If the total
     "unknown" time accounts for more than half the "step", the
     entire PDP is marked as "unknown". This means that a mixture
     of known and "unknown" sample times in a single PDP "step"
     may or may not add up to enough "known" time to warrant a
     known PDP.

     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 5 minutes 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

            u|02|----* sample1, restart "hb"-timer
            u|03|   /
            u|04|  /
            u|05| /
            u|06|/     "hbt" expired
             |08|----* sample2, restart "hb"
             |09|   /
             |10|  /
            u|11|----* sample3, restart "hb"
            u|12|   /
            u|13|  /
      step1_u|14| /
            u|15|/     "swt" expired
             |17|----* sample4, restart "hb", create "pdp" for step1 =
             |18|   /  = unknown due to 10 "u" labled secs > 0.5 * step
             |19|  /
             |20| /
             |21|----* sample5, restart "hb"
             |22|   /
             |23|  /
             |24|----* sample6, restart "hb"
             |25|   /
             |26|  /
             |27|----* sample7, restart "hb"
      step2__|28|   /
             |22|  /
             |23|----* sample8, restart "hb", create "pdp" for step1, create "cdp"
             |24|   /
             |25|  /

     graphics by vladimir.lavrov@desy.de.

How to Measure
     Here are a few hints on how to measure:

         Usually you have some type of meter you can read to get
         the temperature.  The temperature is not really
         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. RRDtool will
         then record your reading together with the time.

     Mail Messages
         Assume you have a method to count the number of messages
         transported by your mail server in a certain amount of
         time, giving you data like `5 messages in the last 65
         seconds'. If you look at the count of 5 like an ABSOLUTE
         data type you can simply update the RRD with the number
         5 and the end time of your monitoring period. RRDtool
         will then record the number of messages per second. If
         at some later stage you want to know the number of
         messages transported in a day, you can get the average
         messages per second from RRDtool for the day in question
         and multiply this number with the number of seconds in a
         day. Because all math is run with Doubles, the precision
         should be acceptable.

     It's always a Rate
         RRDtool stores rates in amount/second for COUNTER,
         DERIVE, DCOUNTER, DDERIVE 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 an absolute
         amount by multiplying by the delta-time between the
         points. RRDtool plots continuous data, and as such is
         not appropriate for plotting absolute amounts as for
         example "total bytes" sent and received in a router.
         What you probably want is plot rates that you can scale
         to bytes/hour, for example, or plot absolute amounts
         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

      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 \

     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 5'000.

     A few archive areas are also defined. The first stores the
     temperatures supplied for 100 hours (1'200 * 300 seconds =
     100 hours). The second RRA stores the minimum temperature
     recorded over every hour (12 * 300 seconds = 1 hour), for
     100 days (2'400 hours). The third and the fourth RRA's do
     the same for the maximum and average temperature,

Example 2
      rrdtool create monitor.rrd --step 300        \
        DS:ifOutOctets:COUNTER:1800:0:4294967295   \
        RRA:AVERAGE:0.5:1:2016                     \

     This example is a monitor of a router interface. The first
     RRA tracks the traffic flow in octets; the second RRA
     generates the specialized functions RRAs for aberrant
     behavior detection. Note that the rra-num argument of
     HWPREDICT is missing, so the other RRAs will implicitly be
     created with default parameter values. In this example, the
     forecasting algorithm baseline adapts quickly; in fact the
     most recent one hour of observations (each at 5 minute
     intervals) accounts for 75% of the baseline prediction. The
     linear trend forecast adapts much more slowly. Observations
     made during the last day (at 288 observations per day)
     account for only 65% of the predicted linear trend. Note:
     these computations rely on an exponential smoothing formula
     described in the LISA 2000 paper.

     The seasonal cycle is one day (288 data points at 300 second
     intervals), and the seasonal adaption parameter will be set
     to 0.1. The RRD file will store 5 days (1'440 data points)
     of forecasts and deviation predictions before wrap around.
     The file will store 1 day (a seasonal cycle) of 0-1
     indicators in the FAILURES RRA.

     The same RRD file and RRAs are created with the following
     command, which explicitly creates all specialized function
     RRAs using "STEP, HEARTBEAT, and Rows As Durations".

      rrdtool create monitor.rrd --step 5m \
        DS:ifOutOctets:COUNTER:30m:0:4294967295 \
        RRA:AVERAGE:0.5:1:2016 \
        RRA:HWPREDICT:5d:0.1:0.0035:1d:3 \
        RRA:SEASONAL:1d:0.1:2 \
        RRA:DEVSEASONAL:1d:0.1:2 \
        RRA:DEVPREDICT:5d:5 \

     Of course, explicit creation need not replicate implicit
     create, a number of arguments could be changed.

Example 3
      rrdtool create proxy.rrd --step 300 \
        DS:Requests:DERIVE:1800:0:U  \
        DS:Duration:DERIVE:1800:0:U  \
        DS:AvgReqDur:COMPUTE:Duration,Requests,0,EQ,1,Requests,IF,/ \

     This example is monitoring the average request duration
     during each 300 sec interval for requests processed by a web
     proxy during the interval.  In this case, the proxy exposes
     two counters, the number of requests processed since boot
     and the total cumulative duration of all processed requests.
     Clearly these counters both have some rollover point, but
     using the DERIVE data source also handles the reset that
     occurs when the web proxy is stopped and restarted.

     In the RRD, the first data source stores the requests per
     second rate during the interval. The second data source
     stores the total duration of all requests processed during
     the interval divided by 300. The COMPUTE data source divides
     each PDP of the AccumDuration by the corresponding PDP of
     TotalRequests and stores the average request duration. The
     remainder of the RPN expression handles the divide by zero

     Tobias Oetiker <tobi@oetiker.ch>, Peter Stamfest
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