My array has 7 disks, all XFS except for 1 Reiserfs (disk3).  Has 1 SSD cache drive, and 1 disk that I'm currently preclearing.

 

Disk 3 won't mount (has red X - says data is emulated).  However, if I go into maintenance mode, I can manually mount it and everything looks fine.

reiserfsck passes.  smart short test passes fine.

I've attached diagnostics.  Don't see anything in syslog telling me why either.....

 

One odd, interesting thing - when I noticed the red X the first time - the number of writes on the drive was a preposterous number - something like

14,000,000,000,000 (yes, 4 commas), which I'm pretty sure wasn't real.  Nothing has been writing to that drive for over a week (it's my smallest drive, and

I use it for my personal pc backup).

How do I find out why it won't mount? 

qnas-diagnostics-20150628-2041.zip

http://lime-technology.com/wiki/index.php/Troubleshooting#What_do_I_do_if_I_get_a_red_ball_next_to_a_hard_disk.3F

There's no indication of a write failure in the log - I would think that would be something you log. Also, nothing is actually writing the disk - it starts off with a red X when the array starts

 

Logs are not preserved though a reboot; however, disk status is preserved. A disk only becomes disabled after a write failure.

Disk 3 won't mount (has red X - says data is emulated).  However, if I go into maintenance mode, I can manually mount it and everything looks fine.

reiserfsck passes.  smart short test passes fine.

I find out why it won't mount?

The reason it probably mounts OK is that you are mounting the emulated disk, not the physical disk.

 

A red-ball state indicates that a write to the disk failed.  Once a disk has been red-balled any further writes only go to the emulated disk - not to the physical disk.  The red-balled state can only be cleared by successfully rebuilding the disk (either back to itself, or to a replacement).