Freenas "/dev/ada0 currently unreadable"

Currently on Freenas 11.1-RELEASE
i3 4170, 16GB ECC, 4x4TB WD RED, RAIDZ2
I have had this machine since 2016 Summer, have never seen this message.

I just received this message in my Freenas Alerts:

Some of my plugins also turned off by itself.
Is scrubbing needed? Run smartctl tests?
Found this page:

Please give any suggestions on what to do.
thank you!!

ada0: smartctl -q noserial -a /dev/ada0