[rrd-users] Re: how to merge 2 rrd-files
Alex van den Bogaerdt
alex at ergens.op.het.net
Tue Jun 8 23:20:54 MEST 2004
On Tue, Jun 08, 2004 at 07:59:23PM +0100, McGlinchy, Alistair wrote:
> Although I agree with your suggestion that using CDEFs adding two rrds
> to build a summed graph is a good idea this does still not remove the
> usefulness of an rrdmerge utility. I am presently working on a perl
> script to merge two rrds together. This is not so much because I want to
> *add* two rrds together, but because I want to update import data.
I do not want to discourage your efforts however I can answer all
three of your example questions. This doesn't mean your script is
worthless, it just means _I_'d do without.
> Example 1:
> You are running MRTG using 32bit SNMP counters and you want to switch to
> 64 SNMP counters. If you just change your configs you will get enormous
> spikes in each graph as the 64 bit counters will be much bigger than the
> 32 bit, but may still be valid data for the RRD. My solution is to run
> MRTG with 64 bit counters and have it create a brand new RRD. Then you
> can merge the old RRD data from 32 bit collections into the new RRD.
Step 1: stop updating using the 32-bit counter
Step 2: insert NaN in the stream (rrdtool update ... N:U)
Step 3: start updating using the 64-bit counter
> Example 2:
> Your collection server crashes and you are in a mad panic. You start up
> collections on a separate server while you fix your server. What do you
> do with the data collected on the backup server when your normal
> collection box is fixed...?
Step 1: update both databases simultaniously (so that they're in sync)
Step 2: a: rrdtool dump database1.rrd > database1.xml
b: rrdtool dump database2.rrd > database2.xml
Step 3: copy interesting parts from both xml files into a third
Step 4: rrdtool restore newdatabase.xml newdatabase.rrd
This is the most complex solution. Then again, how often are you
going to make this mistake?
> Example 3:
> You give up on the crappy SNMP service on Windoze and decide to monitor
> server utilisation via the switch port interface instead. What do you do
> with the old rrd ?
See Example 1, but make sure to switch the inputs
(i.e. "rrdtool update ... N:a:b" becomes "rrdtool update ... N:b:a")
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