Filesystem won't mount because of "unsupported optional features (80)"

[Maurice Volaski]

>  > Filesystem features:      has_journal resize_inode dir_index filetype
>>			    64bit sparse_super large_file
>
>>  What could be causing this error and what does "80" refer to?
>
>For some reason the 64bit feature is set in the filesystem.  This should
>only be set for ext4dev filesystems.  Are you specifying this feature
>yourself e.g. "mke2fs -O 64bit ..."?  Your filesystem is only 2.7TB so
>you don't need the 64bit feature set and it doesn't really help you
>unless you plan to expand the logical volume past 16TB.
>

Indeed, it appears that my initial assumption is correct. mke2fs 
contains ext4dev code and it erroneously applies the 64bit flag to 
filesystems > 2 TB by default. I confirmed this by creating a 1999G 
filesystem and it didn't get the 64bit flag. I then resized it 3000G, 
and luckily resize2fs doesn't contain this code or attempt to adjust 
the flags. The filesystem checked OK in fsck and is now mounting 
properly.
-- 

Maurice Volaski, mvolaski at aecom.yu.edu
Computing Support, Rose F. Kennedy Center
Albert Einstein College of Medicine of Yeshiva University