please help me to understand what this is

I think its related to "fix common problems" addon.

the diagnostics was run before getting the call traces.  

after the error, it was impossible to run the diagnostics. 

 

syslog 13Jan18.rtf

tower-diagnostics-20180113-1749.zip

The trace is being issued during one of FCP's tests, but it isn't going to be caused by it. 

 

I think the most likely cause is some sort of corruption on one of the disks, but its hard to say with any certainty.  If you want to remove FCP, then you can delete /config/plugins/fix.common.problems.plg on the flash drive and reboot the system.

what are the ways to check disk corruptions pls?

I have XFS on data disks and BTRFS on the cache.

 

Here is what I would do.  Since you (apparently) have returned to your previous version, stop the array and make a copy of your flash drive. (This will allow you to always be able to go back to the previous version by copying back the backup without a parity check on restart.)  Next, go the the Plugin page and check to see that all of your plugins are up to date.  

 

Uninstall the Fix Common problems plugin.  (I say this because that plugin is referenced several times both before and after the trace call.)  Now install version 6.4.0 and see what happens.  Look at the Tools  >>>  System Log and search for "error"  and " err"   (note the space) using your browser search feature. 

 

As a favor to the people who want to help you please leave the syslog file with the .txt extension. changing it to .rtf is hassle to handle (especially, it has been actually converted to that format).