[rrd-users] DEF/CDEF Average Question

[Chris Nighswonger]

I have data that I want to average in 15 min windows. The caveat here
is that the windows must start at 0 min, 15 min, 30 min, and 45 min of
each hour.

I can do

DEF:x=foo.rrd:bar:AVERAGE:step=900

But if foo.rrd starts at 5 min past the hour, my window is skewed.

I know I can add ':start=sometime', but I don't see the sort of
"wildcard" syntax needed to do something like ':start=*:00' or some
such to achieve my goal.

I have worked with TRENDNAN, but I'm not looking for a sliding window,
but one which resets every period.

Kind Regards,
Chris