Some say that it is only 25 gig after being formatted?

Well, first there's the manufacturers habit of counting 'kilo' as 1000
instead of 1024...

30.000.000.000 / 1024^3 =~ 27,94

Then you'll use some for the filesystem (inodes etc). I don't recall
what inode density (though I believe it's been posted) empeg uses on
the data partition. Too high inode density wastes space to inodes
that'll never be used, to low wastes space by allocation a large chunk
of disk to every little file, ie the xx1 files.

Given an assumtion of the average size of the two filetypes (xx0 and xx1)
the optimum density could be calculated, but I'm way to tired to try it
now...

/Michael