Ok, I've been beating my head on this...
I'm trying to do 1 minute polling with 0.8.7. I am relatively new to cacti, had previously been using 0.8.6j. I started working on 1 minute polling a few days before 0.8.7 was released.
So, I've dumped everything and am starting afresh with 0.8.7.
I have a few questions about understanding the out of the box settings, and how to modify this for 1 minute polling operation. If you find them tiresome, please skip to the end of the post.
Out of the box, there is both a 5 minute RRA ["Daily (5 Minute Average)"] and a 1 minute RRA ["Hourly (1 Minute Average)"].
The 5 minute RRA ["Daily"] uses a step value of 1, which assuming the default polling interval of 5 minutes seems to make sense. The 1 minute RRA also uses a step value of 1, which seems to make sense if the polling interval is changed to 1 minute.
The 5 minute RRA ["Daily"] uses a timespan of 86400 [1 day], which seems to make sense. However, the 1 minute RRA ["Hourly"] uses a timespan of 14400 [4 hours], which doesn't make sense to me. Why is this?
The 5 minute RRA ["Daily"] allocates 600 rows, which assuming the default polling interval of 5 minutes would be a timespan of 50 hours. Why isn't the default number of rows for the 5 minute RRA 288 (24 hours)?
The same question applies to the rows in the "Weekly", "Monthly", and "Yearly" RRAs. They appear to allocate more than twice the number of rows needed.
The 1 minute RRA ["Hourly"] allocates 500 rows, which assuming a polling interval of 1 minute results in a timespan of 8.3 minutes. This would seem to wrap/overwrite very quickly Why wouldn't the default number of rows be 3600?
Am I just missing something basic on the math???
The timespan on the "Yearly" RRA is 33053184, which is 382.56 days. Why isn't the timespan 31536000 (or 31557600)?
So, with all the confusing background questions out of the way, the real question is how to set the RRAs up correctly for 1 minute polling?
Ignoring the default values at install, I would have assumed this:
Name Steps Rows Timespan
Hourly (1 Minute Average) 1 3600 3600
Daily (5 Minute Average) 5 17280 86400
Weekly (30 Minute Average) 30 20160 604800
Monthly (2 Hour Average) 120 22320 2678400
Yearly (1 Day Average) 1440 21915 31557600
Yes, now that I write it out, the number of rows seems rather large.
I'm sure I've got some basic concept wrong, and I would appreciate someone correcting my math.