High latency when adding shelf

• ONTAP 9
• DS224C

• high latency (around 80ms) in a short while right after hot-adding a new disk shelf (DS224C)
• The EMS logs, the 3 drives report shm.threshold.agrsvIOCount. We do not see any latency on the other drives on the same shelf 12.

[?] Tue Jul 04 13:33:53 +0900 [t1-tnfsto-s02-node2: disk_server_0: shm.threshold.agrsvIOCount:notice]: Disk 5a.12.0 has exceeded 12 IOs which have latencies greater than the threshold.

[?] Tue Jul 04 13:33:58 +0900 [t1-tnfsto-s02-node2: disk_server_1: shm.threshold.agrsvIOCount:notice]: Disk 5a.12.2 has exceeded 12 IOs which have latencies greater than the threshold.

[?] Tue Jul 04 13:33:58 +0900 [t1-tnfsto-s02-node2: disk_server_0: shm.threshold.agrsvIOCount:notice]: Disk 5a.12.10 has exceeded 12 IOs which have latencies greater than the threshold.

• Shelf 13 has different firmware versions on module A and B.

Shelf 13: DS224-12 Firmware rev. IOM12B A: 0120 IOM12B B: 0100