3270 cluster, OnTAP 8.1-7mode
We are investigating a SATA aggregate showing repeated 5am disk 100% busy spikes without its volumes showing any corresponding IOPS spike as reported by Netapp Management Console (NMC).
The 5am disk busy spikes correlate with very high latency on volumes on a different SAS aggregate. These volumes host VMs which then timeout, some needing reboots.
Today when I heard from Netapp support after reviewing my perfstat the engineer reported this is expected since NVRAM buffers are shared btw aggregates.
But when I dig further into the NMC stats I see the SATA aggregate disk busy actually corresponds to a DROP in IOPS on the 3 volumes hosted on the SATA aggregate - almost like some internal aggregate operations are starving out the external volume ops.
I checked the snapshots (vol and aggr), snap mirror, dedup and none of the usual suspects were running.
When I look at the NMC throughput graphs and switch on the legend - it shows a 5am READ blocks/sec spike corresponding perfectly to the disk busy.
Where are these AGGR level READ operations coming from that are missing from the constituent volume IOPS, and in fact seem to be starving out volume level IO?
I don't see much in the messages log, but will check the rest of the logs for internal type OPS