I ran a 1 second and 30 second write monitor on the same volume and compared stats.  It appears that this measurement is the average write rate over the specified period.  For a given 30 second interval using the 1 second file data, the peak KB/sec rate was 4412, the total transferred was 20176, and the average was 20176/30 or 672.53333.  The 30 second file shows a rate of 673 for this interval.  So for calculating average utilization a long interval may work but for peak utilization the shortest interval possible would be better.
I am trying to monitor writes to a virtual volume in order to calculate WAN bandwidth utilization after mirroring.  I'm confused on the units being reported, though.  I'm setting up the virtual-volume.writes monitor every 5 seconds and a file-sink.  Then I'm using the CSV output and charting with Excel.  The data collect and charting works great.  However the units reported are supposedly Kilobytes per second.    What does this mean exactly for a 5 second (or 30 second, or 5 minute) collect?  Is this total number of Kilobytes written throughout the collect period?  Is this an average KB/sec write rate throughout the period?  Is this the maximum KB/sec write rate during the time period?  It is odd to me because you don't generally have a per second write rate in a cumulative counter.    Thanks for any clarification on these units.
VPLEX Monitor counter units - KB/sec