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

Maurice Volaski mvolaski at
Sat Feb 17 22:53:56 UTC 2007

>  > 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 

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

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