So, I have a customer with a FAS2520. Been running in production for a few years now on ontap 9.0.
We did an upgrade today to ontap 9.2.
While poking around I noticed the Flash Cache screen said the controllers had 768GB of flashcache disabled. So I went ahead and hit the enable button in the GUI for both controllers.
Now, I'm pretty certain the FAS2500 series did not have flash cache as an option and a sysconfig from both nodes doesn't show anything.
So where did this phantom flash cache come from? The really weird thing the flash cache screen will even show an occasional hit.
Does 9.2 show the NVMEM or something weird as flash cache?
At this point the fix is pushed back further than 9.4 - It's a low priority issue, since there isn't any chance of data corruption or system instability, and fixing it is a surprisingly involved task.
OCSM trusts the zAPI to describe what capabilities the controller has and draws the UI on that basis, and the zAPI trusts the flashcache management module, and flashcache trusts the controller to not describe anything it doesn't have, but the controllers can ship with different configs of flashcache (zero on AFF vs FAS with 1 or 2 cards depending on config and any hardware errors), so they don't validate that component at boot.
If it is a significant concern, I would encourage you to log a case and ask that it be recorded against BURT 1131025 and 1122144.
Really thankful for this thread, as I just upgraded to 9.3P10 (from 9.2P4) and noticed the Flash Cache entry on my AFF system. Although low priority, I would note that these unusal anomolies do waste some time for administrators. I spent some time researching online and this message board post was the only content I found that answered the question.