[collectd] Changing recording resolution

[collectd_mlist at indiv.spillett.net]

I'm looking to increase the long-term resolution of some (or all) or my collected data. I manage to confuse myself at one point  while looking through various things (collectd documents, RRDTool man pages and various Google finds) so I'd like to confirm my understanding before I go making changes...



Firstly:

Am I right in thinking that if I simply set "RRARows 8928" it will keep up to 8928 derived samples for each reading for each of the five default time periods, so there will be one sample every 5 minutes in the "31 days" RRAs (31*24*60/8928==5).

I appreciate that this is going to bump up the size of the resulting data files by a factor of approx 8 over the default "RRARows 1200", and this shouldn't be a problem unless it is likely to make rrdtool noticeably slower. To reduce the size difference if I can though, is it possible to set RRARows on a per-plugin basis (I'm only wanting it particularly for the network interface and iptables plugins at the moment).



Secondly: 

Am I right in assuming that I'll need to remove the rrd files so collectd recreates them with the new settings, and that there is no easy way to import the data from the old files? (it would be nice if I could copy data derived from the old files into the new ones, but far from essential as I can just keep the old ones for reference in case anyone asks me to provide graphs from old data).



In case it makes any difference to the questions above: I'm using a pretty up-to-date collectd (4.4.1, the latest in the semi-official backports repository for Debian/Etch) and rrdtool from the standard Etch repository.



Thanks in advance,
(and thanks in general for creating a very useful tool)
Dave.