Ext4 64bit mode

[Stephan Hegemann]

Hi, I recently heard about the 'old' ext4 > 16TB problem, which seems to 
be related whether the filesystem was created with or without 64bit support.

I checked my Ubuntu-Desktop /home Filesystem (created with 14.10 amd64, 
with lvm) and the root filesystem of a Ubuntu-Server 15.04 installation 
(amd64, lvm enabled, standard partitioning) and both seem to lack the 
'64bit' flag, which indicates the ability to exceed the 'magic 16TB' 
(http://www.reddit.com/r/DataHoarder/comments/1uxg3r/til_cant_grow_ext4_past_16tb_without_o_64bit/)

Desktop:
Filesystem features:      has_journal ext_attr resize_inode dir_index 
filetype needs_recovery extent flex_bg sparse_super large_file huge_file 
uninit_bg dir_nlink extra_isize

Server:
" Exactly the same

Test Filesystem made with 'sudo mke2fs -t ext4 -O 64bit':
Filesystem features:      has_journal ext_attr resize_inode dir_index 
filetype extent 64bit flex_bg sparse_super large_file huge_file 
uninit_bg dir_nlink extra_isize


I used the standard partitioning tools from the installer.
My Question is, why wasn't the Ext4 filesystem created in 64bit mode per 
default? Personally I don't need more than 16TB, and for a Desktop 
installation it probably isn't necessary. But on a 64bit Server with lvm 
in use, I don't see a problem in creating a future-proof Ext4 with 64bit 
flag.

Greetings, Stephan Hegemann