We have an MRTG installation that has been working for the last 3 years, I noticed that after 18 or so months the data would start recording a fresh. Now I wanted to transfer the installation and all the graph data, is it possible to transfer this data to a new installation? What is the procedure for doing this. The Installation has been done on a Freebsd 8.0 and the new one is Freebsd 10.0
MTRG has two different backends. The old style backend that uses a text file, and you can use a newer backend that uses RRD files. RRD files are architecture specific, and even somewhat version sensitive to the version of rrdtool in use. So if you are using RRD as your storage method, you may need to go through an export/import process where you extract the data on a source system, and then create new RRD files on the destination system.
If you are using the original storage format, it should be as simple as transferring the configuration, and all the data to the new system. Assuming you transfer everything, and get all the required software for mrtg installed, it should just work.
In any case the easiest way to find out will be to just try it. I haven't used mrtg on freebsd, but I have it a lot on Linux systems.