[Xymon] [xymon]repair rrd data

Hello

I have many ncv graph and they often "dotted" instead made of lines It's like some data left in rrd : see attachment

• How to correct without loosing all data ?
• how it's happened ?

I had search for "rrd repair tools" but nothing seems works on my server or PEBCAK ;-)

(hope my english is not too bad)