ONTAP v9 bug
There is a problem with ONTAP v9 firmware which however might not affect all v9 instances.
Storage firmware 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-):
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!
There is nothing else we can do.
NetApp native tools for perf monitoring are not affected as they use other interface.
We have choosen this interface as it was only the way which did not require admin access for getting perf data at time we have wrote implemented it.
We are going to implement other method to get performance data from NetApp by usage OnCommand-API-services, OnCommand Performance Manager and OnCommand Unified Manager products.
It is already developed and being tested, expected at the end of Q4 2018.
Note this bug appears only on minor number of NetApp C-mode storage, 7-mode does not seem to be affected at all.
Apparently this issue might be fixed or at least appears much less in ONTAP v9.3.