On 2/7/20 7:49 AM, o1bigtenor wrote:

Greetings

Running a Raid-10 array made up of 4 - 1 TB drives on a debian testing
(11) system.
mdadm - v4.1 - 2018-10-01 is the version being used.

Some weirdness is happening - - - vis a vis - - - I have one directory
(not small) that has disappeared. I last accessed said directory
(still have the pdf open which is how I could get this information)
'Last accessed 2020-01-19 6:32 A.M.'  as indicated in the 'Properties'
section of the file in question.

I assume you've looked at lsof?

https://www.linux.com/news/bring-back-deleted-files-lsof/

If it is a software problem, it just as likely, if not more likely, that it is a file system problem rather than a raid problem. You don't mention 
what file system. You're possibly also actually looking at data in the in-memory disk cache rather than what's actually stored on disk given there's 
been no reboot.

Is there anything suspicious in dmesg?