Permanent errors in kernel after upgrade to 9.10.2

[meekjt13]

After upgrading to 9.10.2 there was an error indicated in the web ui, to get more information I ran "zpool status -v" from the console and got the following output:

Code:

pool: freenas-boot
state: ONLINE
status: One or more devices has experienced an error resulting in data
	corruption.  Applications may be affected.
action: Restore the file in question if possible.  Otherwise restore the
	entire pool from backup.
   see: http://illumos.org/msg/ZFS-8000-8A
  scan: scrub repaired 245K in 0h13m with 1 errors on Fri Dec 23 08:03:03 2016
config:

	NAME		STATE	 READ WRITE CKSUM
	freenas-boot  ONLINE	   0	 0	 0
	  mirror-0  ONLINE	   0	 0	 0
		da0p2   ONLINE	   0	 0	 0
		da1p2   ONLINE	   0	 0	 0

errors: Permanent errors have been detected in the following files:

		freenas-boot/ROOT/9.10.2@2016-05-03-06:22:02:/boot/kernel/kernel

This was the first time I encountered an error on FreeNAS so I thought I should be able to roll back to a previous boot environment to solve the problem. It turns out that any boot environment I change to has the same error, but with the active boot environments kernel file.

I'll now reinstall from scratch to fix the problem, but I'm quite confused as to what is happening here. My questions are:

1. Why doesn't the output of "zpool status -v" report errors in non-active datasets?
2. How can the same file be damaged across multiple datasets?
3. Since by boot device is a mirror across two drives how could this error have happened? Shouldn't ZFS prevented a file from becoming corrupt? I know it's theoretically possible, but isn't it highly unlikely in this configuration?
4. Would increasing the number of devices in the pool mirror help prevent this from happening again?

Thanks for any help, I'm mainly curious in knowing what might have happened here.

EDIT: The other odd thing is that the system boots and works as usual, I didn't expect that to be possible if the kernel file has error.

 

[Jailer]

It's not a kernel error, your boot device is failing.

 

[Ericloewe]

Reinstall to new media and upload your config file. If you don't have a backup, make one now.