Well 64Z is roughly 70,250,000,000,000G so yeah, 71G is going to be considerably
less than 1% lol
Personally if you've the budget for that amount of drive space you can afford to add a few more!
On a more serious note the OP needs to carefully check the output they are getting from df and compare it to something like du for the volume. Getting results returned in the Zb range would indicate something is wrong.
Also remember that ext3 reserves some space for root so that even if the drive shows 100% full there is still some free space. From memory it's 5%