munin rrd merge history

merge.sh

#!/bin/bash

$ip_old_munin_server = '192.168.0.200'

mkdir -p /backup/old

for filename in /var/lib/munin/*/*/*.rrd; do
        if [ ! -f "/backup/old/$(basename "$filename")" ]; then
                echo $filename
                ssh $ip_old_munin_server "rrdtool dump $filename" | rrdtool restore - "/backup/old/$(basename "$filename")"
                mv $filename "${filename}_before"
                python simple-rrd-merge.py "/backup/old/$(basename "$filename")" "${filename}_before" | rrdtool restore /dev/stdin $filename
                chown munin:munin $filename
        fi
done

uses the following python script:
https://gist.github.com/arantius/2166343

script is only for quick&dirty migration.