2**31-1 blocks question

[Mag Gam]

We need to create very large filesystems. We prefer to have a
filesystem which is 12TB but it seems ext3 does not suppor that.

Everytime, we do mkfs.ext3 on a 12TB LV we get

mke2fs: Filesystem too large.  No more than 2**31-1 blocks

         (8TB using a blocksize of 4K) are currently supported.


We can override that by doing,

mkfs.ext3 -b 8192

But what is the downside for doing this? By using a larger blocksize
what are the consequences?