Matthew Chambers wrote:
I recently discovered the solution to a problem I was having and want
some more detail. I initially set up gmetad.conf with my data sources
using default intervals (15sec). I then decided I wanted 10sec
intervals so I changed the conf and restarted the service. I soon
discovered that my hour graphs looked like bar graphs. After much
gnashing of teeth (and learning about rrdtool, and help from
#rrdtool), I discovered that the default RRAs that were initially
created by gmetad were dependent on the 15sec interval (actually, >=
15 sec). In other words, the RRA for the hourly data was not big
enough to store 10 second intervals because it was created for 15
second intervals; as a consequence, the next largest RRA was used, the
daily RRA which had ~24 times lower resolution! It seems to me that
when gmetad starts up, it should check the RRAs and should either warn
that the existing RRAs are too small or it should resize the RRAs
automatically. Is this a known issue?
Thanks,
Matt Chambers
Matt Chambers,
This specific issue is not captured to my knowledge, but that it would
happen is expected and can be explained by Bug 33
<http://bugzilla.ganglia.info/cgi-bin/bugzilla/show_bug.cgi?id=33>. I do
know of two things that will help you.
1. Jason wrote a perl script
<http://bugzilla.ganglia.info/cgi-bin/bugzilla/attachment.cgi?id=19&action=view>
that will tune and resize all of your RRD's.
2. You can specify your own RRA spec in gmetad.conf to store more data.
Look to rrdtool for better documentation on what the RRA spec means. The
default based on 15 seconds looks like this:
RRAs "RRA:AVERAGE:0.5:1:244" \ #one sample every 15 sec for 61 min
"RRA:AVERAGE:0.5:24:244" \ #one sample every 6 min for 24.4 hours
"RRA:AVERAGE:0.5:168:244" \ #one sample every 42 min for 7.11 days
"RRA:AVERAGE:0.5:672:244" \ #one sample every 168 min for 28.4 days
"RRA:AVERAGE:0.5:5760:374" #one sample every day for 374 days
(remove the comments and put on one line)
Cheers,
Ian C.
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