Resizing a file system that has been converted to ext4

Hello,

I have an ext3 file system of about 8TiB in size.  At the rate data is 
added to the file system it will fill up in a few months so I'm weighing 
my options.  One option would be to create a new ext4 file system and 
copy everything over to a new, larger ext4 file system.  Another option 
would be to modify the software that uses this file system so it can use 
multiple file systems.  Finally, I could could convert the existing file 
system to ext4 and then resize it.  Is this advisable?  Has anyone tried 
this?

Thanks,
Sean McCauliff