[rrd-users] Re: rate of change

[Stephan Harren]

How about using PREV?

You can CDEF:oldvalue=actualvalue, oldtime=TIME. Then you can use 
CDEF:roc=actualvalue,PREV(oldvalue),-,TIME,PREV(oldtime),-,/

Best regards and HTH,

Stephan

> assumption:  ROC = (y1 - y0) / (x1 - x0)
>
> my rrd is a gauge of disk space used in bytes.
> i assume all I need is to keep the first byte value (y0)
> and first timestamp (x0), then cdef it like this:
>
> CDEF:roc=y1,y0,-,TIME,x0-,/
>
> but howto save first values (time = x0, bytes = y0)?
> this doesnt work:
>
> CDEF:y0=y0,UN,used,y0,IF
> CDEF:x0=x0,UN,TIME,x0,IF
>
> Howto save first values?
> any other suggestions for ROC calculation?
-- 
Stephan Harren
Manager Site Operations
AboveNet Deutschland GmbH
-------------------------------
Phone +49 69 90554 153
Fax +49 69 90554 111
Cell +49 173 7011126

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