Updating values in an existing RRD file

Question

I have an rrd file working fine under cacti, drawing a graph for me for more than a year from one data source.

Today, I discovered that the data in the rrd file is not correct. I have corrected the data source and fixed problem for the future. However, I need to divide the previous data by 2 to correct it historically as well.

Is it possible to update the values of an rrd file? If yes, how can I achieve this?

This might help: https://stackoverflow.com/questions/10298484/remove-data-from-rrdtool — zedfoxus, Jul 18 '18 at 05:30

score 1 · Accepted Answer · answered Jul 18 '18 at 20:56

1

Data in the RRAs cannot be directly changed once written.

However, what you can do is to dump the data to XML (using rrdtool dump); edit it using some other method; and then reload the data into a new RRD file (using rrdtool restore). This, of course, requires you to create some method to automatically modify the values in the XML file, but this should be simpler than trying to modify the RRD directly.

answered Jul 18 '18 at 20:56

Steve Shipway

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thanks! it worked but it was really tricky as I had to modify some of the values based on the date but rrddump had the epoc timestamp. so I backed up the rrd file, dumped into an xml, ran a python script to modify the whole file, and restore. no issues, cacti is writing into new rrd file and graph looks good with new values. thanks again!!! – takobaba Jul 20 '18 at 01:57

Updating values in an existing RRD file

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