ANSWER:

You can’t that’s not how ext4/3/2 works. If you have an odd block size then you will have fewer inodes and even really tiny files take 1 inode. So back in time, which makes copies of things will eat inodes till your out.

Now most of the time, you will run out of free space long before you run out of inodes. However that depends on block size. If you have a 1 gig block size (totally bogus but just go with it) your only going to be able to have 250 files/inodes on a 250 Gig hard drive. If you really want to correct the problem then reformat the file system and use a smaller block size. For back up dives I usually use mkfs -j -i 1024 -b 1024 -I 256 but that’s just me.

coteyr from http://askubuntu.com/questions/297922