[rrd-users] Re: A beginners question

[Jason Fesler]

> Is there a limit to number of RRAs that can be stored in a single
> rrd file?  Are there performance fall offs once you get above a
> particuler number of RRAs in a single rrd?

DS and RRA counts are stored as "unsigned long".  Virtually unlimited.
You're going to run into other limits before you run into the hard RRA
limit of 4294967295.  Your .rrd file size, depending on your OS, has a
maximum file size of 2 gigs.

As to the performance..  I can *definately* say that each RRA adds that
much more IO requirements.  I have 10 RRA's in most of my .rrd files.  I
had to throw a lot of money at the RRD box in terms of disk spindles to
stay with the company's policy on operating system choices.  I am
currently tracking 65000 values (most of those, per-minute), for a total
of 650000 RRA's.  I've had to toss two hardware raids at this
(16 spindles for RRD, non-raid spindles for the OS etc).  According to
iostat, on *average* this hardware is about 45 %b.   CPU on average is 50%
idle, 25% IO wait, and 25% busy.

Note, I only draw graphs on-demand.  Before, when we ran some of the
graphs always, we required a second e450 with a similiar disk
configuration.  I suggestion (strongly) that unless you have a compelling
reason to generate static images.. don't.  It'll burn away at your
capacity very quickly.



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