[rrd-users] Use of LAST within RRA

Lyle Brooks brooks at deseret.com
Thu Feb 4 18:32:11 CET 2010

I am wondering about the proper use of LAST within an RRA.

When I create an RRD file, I use the following definitions...

rrdtool create filename.rrd \
    --step '300' \
    'DS:total:GAUGE:600:0:U' \
    'RRA:AVERAGE:0.5:1:576' \
    'RRA:AVERAGE:0.5:6:672' \
    'RRA:AVERAGE:0.5:24:744' \
    'RRA:AVERAGE:0.5:288:730' \
    'RRA:MAX:0.5:1:576' \
    'RRA:MAX:0.5:6:672' \
    'RRA:MAX:0.5:24:744' \
    'RRA:MAX:0.5:288:730' \
    'RRA:LAST:0.5:1:576' \
    'RRA:LAST:0.5:6:672' \
    'RRA:LAST:0.5:24:744' \

I admit, I simply used 'cut-n-paste' based off what I did for the
AVERAGE and MAX consolidation functions, but as I reflect on the LAST
consolidation function, I find my self asking...

1) Do I need to keep so many rows of LAST points?  or could I get
away with only 1?  I mean, there's only one "LAST" point, yes?

Could I use these lines instead?

    'RRA:LAST:0.5:1:1' \
    'RRA:LAST:0.5:6:1' \
    'RRA:LAST:0.5:24:1' \

2) Do I need 4 RRA's with LAST?  Or do I really only need one?
If so, do I use the higher resolution RRA (ie. no consolidation)
or the lower resolution RRA (ie. consolidate on a 1 day average)?


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