[rrd-users] various questions on rrdcreate/rrd_create

[Rick Jones]

On Wed, 2011-04-20 at 23:28 +0100, Simon Hobson wrote:
> Rick Jones wrote:
> Where there is a likelyhood of the number of datasets changing then 
> you are better off with separate files. An example of that would be 
> monitoring disk space where you may add or remove a filesystem. In 
> that case you'd probably want one file per filesystem.
> On the other hand, for an ethernet interface, I'd have combined those 
> separate files into one since the set of values being logged isn't 
> likely to change.
> 
> Another factor is whether all the data values are going to be 
> available at the same time. You cannot do a partial update - so you 
> cannot update one dataset at one point in time, and another at a 
> different time, when they are in the same RRD file. If you can 
> collect all the data values at once (which would be the case with an 
> ethernet interface), then it's one call to update them all rather 
> than updating each separate file individually.

Thanks.  I was wondering about ntop's decision there since with sflow
counter samples one either gets all of the interface counters or none of
them.

> >Also, when creating with --no-overwrite, what happens if the second or
> >Nth create has a different value for things like step or heartbeat?  Are
> >they simply ignored or does some sort of "conversion" take-place?
> 
> If you don't overwrite the file, then nothing gets changed.

Which explains why, even when I set the primary step to 1 in ntop,
things were still at 300 since I didn't blow-away any of the RRDs.

thanks,

rick jones