Philip Peake wrote: >2. I now understand the "spike" - I assumed that any loss of >connection would mean that the data source was being re-started, and >that counters would start again from zero. What I must have seen >when I saw this occur "naturally" must have been a network problem, >which simply broke the connection, and the counters carried on >running. I need to try to account for that somehow ... hard to know >how really. I suppose I can store previous values, and when the DS >comes back online check to see if the value is less than the >recorded value, in which case assume a restart.
I did have a suspicion that might be your problem - hence why I wanted to see your input data. As it happens, once you saw it, you spotted it too. What I would do is keep adding NaN rather than zero while the data source is unreadable. To my mind, it's more accurate - until you can read the source the data is unknown, not zero. If you do that, then the spike will disappear since the first true reading will simply set a base value to compute the next rate from. If you really want to store zero, then you could : update at t-1 with zero - this will a;most fill the previous slot with zero update at t with Nan - close the previous slot, 29/30ths of which will be zero and so the result will be zero update at t+1 with x Your first computed reading will still be out by 1/30th because the update at t+1 will "lose" 1 second of your 30 second slot - making the rate calculation (x2 - x1) / 29 instead of (x2 - x1) / 30. >3. I really wanted the stored values to be the same as the input >values. They obviously are not, which seems odd since the sample >period is 30 seconds, and I take great care to ensure that the >values sampled as close to 30 seconds apart as I can, and then >entered with a time set to a 30 second boundary. I thought this >should ensure that the stored value would be precisely the >difference between the current and previous value. Can you point out anomalies ? I've had a very quick look and the numbers seem about right to me. You do understand that RRD tool only ever stores rates don't you ? Ie, updates of : 1287866340:80740899 1287866370:80741789 80741789 - 80740899 = 890 890 / 30 = 29.667 value stored : 1287866370: 2.9666666667e+01 -- Simon Hobson Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed author Gladys Hobson. Novels - poetry - short stories - ideal as Christmas stocking fillers. Some available as e-books. _______________________________________________ rrd-users mailing list [email protected] https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users
