Unable to locate old data in rrd file

[maneeshkumarnp]

Would like to understand the way the data is rolled up in rrd file.

ex: The yearly data (1 day average) is kept for 2 years, after completion of the 2 year will the data get purged and start a fresh collection . or it will keep old data and start truncating now - 2 years ?

Thanks and Regards

[TheWitness]

The RRDfile format is a first in first out queue design. So as you insert rows, old rows roll off the stack. It's as simple as that.

In Cacti 1.0 and above we gave the ability to define custom ranges for each round robin archive. You may alter them afterwards using the rrd tool tune command however it will leave gaps in certain graphs depending upon which round robin archive you choose to update. Others on these forums have written utilities to fill those gaps with data. However we have not released a formal tool for doing so to date.

[maneeshkumarnp]

Thank you for the reply.

I do understand that the rrd is a round robin database and old data will be truncated as and when new data comes in

However in our scenario, all of a sudden the old data is completely purged and new collection started for a graph which is more than 2 years. I wanted know if there is any setting to change this behavior. We need to keep 2 years data from now.

[TheWitness]

Yes there is, but you need to first understand how rrdtool works and then configure Cacti to keep the amount of data you want.