topic Re: Mystery Flash Cache after 9.2 Upgrade with FAS2520 in ONTAP Discussions

Mystery Flash Cache after 9.2 Upgrade with FAS2520

Matt99 — Wed, 04 Jun 2025 14:55:25 GMT

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?

Re: Mystery Flash Cache after 9.2 Upgrade with FAS2520

Jeff_Yao — Mon, 03 Jul 2017 01:07:30 GMT

looks like a bug.

Re: Mystery Flash Cache after 9.2 Upgrade with FAS2520

WillFulmer — Sat, 09 Dec 2017 01:02:40 GMT

Seeing same behavior here on systems without FlashCache, including A200 AFA All Flash.

Re: Mystery Flash Cache after 9.2 Upgrade with FAS2520

MattWhite — Thu, 21 Dec 2017 19:21:42 GMT

I'm seeing the same thing with AFF A200. After upgrading to 9.2P1 it shows a flash cache is installed and it let me enable it.

Re: Mystery Flash Cache after 9.2 Upgrade with FAS2520

wertk — Wed, 24 Jan 2018 17:26:33 GMT

I saw the same with an A200 on 9.3RC1. I dug through documentation and bugs but didn't find anything useful.

Re: Mystery Flash Cache after 9.2 Upgrade with FAS2520

FreddieHFS — Thu, 29 Mar 2018 18:07:17 GMT

Seeing this on FAS8020s as well. Interesting...

Re: Mystery Flash Cache after 9.2 Upgrade with FAS2520

MikeSchaus — Thu, 26 Apr 2018 17:23:49 GMT

The same with a aff200 and 9.3. Support said it should be a bug and maybe fixed in 9.4
BUG 1131025

Re: Mystery Flash Cache after 9.2 Upgrade with FAS2520

AlexDawson — Fri, 27 Apr 2018 07:51:31 GMT

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.

Re: Mystery Flash Cache after 9.2 Upgrade with FAS2520

TMADOCTHOMAS — Mon, 04 Mar 2019 15:40:54 GMT

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.

Re: Mystery Flash Cache after 9.2 Upgrade with FAS2520

AlexDawson — Tue, 05 Mar 2019 07:06:36 GMT

Hi @TMADOCTHOMAS - Thanks for your feedback!

Based on my reading of the bug notes, it should be fixed in ONTAP 9.5P1 (released last week)

Re: Mystery Flash Cache after 9.2 Upgrade with FAS2520

TMADOCTHOMAS — Tue, 05 Mar 2019 14:55:55 GMT

Thank you @AlexDawson !