Please help me resize my ext4 file system to size > 16TB

[Ram Ramesh <rramesh2400@gmail.com>]

Hi,

  I have kernel 3.13 and e2fsprog 1.42.9 (as part of mybuntu 14.04.5 
LTS). With this, is it possible to resize2fs my ext4 RAID6 /dev/md0 to 
24TB (ie >16TB)? If so, please help me get there. If not, please 
recommend the upgrades needed to the setup before this can be done. So, 
far, my google says I need to do "tune2fs -O extents,uninit_bg,dir_index 
/dev/md0" which I already did and I still get the dreaded message 
"resize2fs: New size too large to be expressed in 32 bits."

There are mentions of a 64bit option for the ext4 file system. I can see 
how this relates to the error message from resize2fs, but I do not know 
what I should do to get that update done for my /dev/md0. Also all of 
the message that I come across relating to 64bit option, only talk 
about  how to *create* a brand new file system with 64bit. None of them 
tell me how to convert existing one. In fact, many of them scare me 
saying that it will be unsupported in older kernels. I am not really 
sure if my kernel is too old or not. Also, they talk about a switch -b 
for resize2fs that is not supported in the version installed currently 
on my system/release.

Pleas help me figure out the correct sequence of steps. What packages 
need update, if current kernel/release is ok? Or, do I need to upgrade 
to a newer release before this is possible?

Thanks
Ramesh