ONTAP v9 bug
There is a problem with C-mode ONTAP v9 firmware which however might not affect all v9 instances.
Apparently this issue might be fixed or at least appears much less in ONTAP v9.3+
Storage CLI reporting very high utilization peaks randomly for different volumes/aggregates/port etc.
When we detect such data then we throw away whole data collection what results in data gaps.
You can see similar messages in storage error log (logs/error.log-<storage alias>):
ERROR Thu Mar 22 14:40:11 2017 naperf.pl: Bad NetApp data detected! Collection ignored... SUBSYS: aggregate NAME: Netapp01 METRIC: read_data VALUE: 17084398071KB
It is a confirmed NetApp bug 1091745
As per last information NetApp not going to fix it!