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

Maurice Volaski mvolaski at
Sat Feb 17 08:38:02 UTC 2007

>On Feb 17, 2007  01:32 -0500, Maurice Volaski wrote:
>>  I made a filesystem (mke2fs -j) on a logical volume under kernel
>>  2.6.20 on a 64-bit based system, and when I try to mount it, ext3
>>  complains with
>>  EXT3-fs: dm-1: couldn't mount because of unsupported optional features (80).
>>  I first thought I just forgot to make the filesystem, so I remade it
>>  and the error is still present. I ran fsck on this freshly made
>>  filesystem, and it completed with no errors.
>>  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.
>If you do need this functionality then you need to use the ext4dev
>filesystem, but this is currently a work-in-progress and shouldn't
>be used for critical data.

I have no idea how it got there. I make the filesystem with mke2fs -j 
and the mke2fs.conf lists "base_features = 
sparse_super,filetype,resize_inode,dir_index". I do not have ext4dev 
compiled into the kernel at all. My other filesystems, all under 2 
TB, seem to be working, so I wonder whether somehow some ext4dev got 
erroneously added to ext3, and it's being applied to filesystems that 
are greater than 2 TB and are being compiled with 64-bit gcc, just a 
wild guess on my part.

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

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