High latency after ONTAP reboot due to malfunctioning Flash Cache

Applies to

Issue

High latency observed right after ONTAP reboot with the following symptoms:

• Increasing disk util
• Higher delay from Disk IO 
• No hits from Flash Cache (ext_cache). Example:

::> system node run -node node_name stats show -p flexscale-access
Cache                                               Reads         Writes          Disk Reads
Usage Hit   Meta  Miss    Hit  Evict  Inval  Insert Chain  Blocks Chain   Blocks  Replaced
%     /s    /s    /s      %     /s    /s     /s     /s     /s     /s      /s      /s
45    703   11    39171   1     0     0      0      0      0      0       0       109
45    320   26    37607   0     0     0      0      0      0      0       0        98
45    903   51    38018   2     0     0      0      0      0      0       0       114
...

• The Flash Cache card status is ok in sysconfig -a 

	slot 1: Flash Cache NVMe
		Serial Number:      ZEP00GPR
		Part Number:        119-00329
		Hardware Revision:  A0
		Firmware Version:   NA03
		Model Name:         X3311A
		Capacity:           1024 GB
		State:              ok

Notes:

• This symptom is pretty close to what is described in Bug 1164008, though it's already on a fixed version.