Hi,
I have a small problem with my home partition. The size of the partition (ext4) is ~895GiB. I’m using ~77GiB of the partition but still the Dolphin shows me that I have 773 GiB free (so according to my calculations I’m missing ~45GiB).
I’ve looked everywhere but I don’t understand where did the missing space go.
Thank you.
Have a read of that;
Filesystems (ext3, reiser, xfs, jfs) comparison on Debian Etch
On EXT filesystems some space is reserved for root. It can be changed.
boncey.org - Reclaiming ext3 disk space
I’ve heard of dodgy things happening if you drop much below 5%. But then, that might depend on absolute size too - and I don’t think your system would suddenly blow up (it might just run really slowly, for example…)
Still - don’t turn it off entirely, eh? 
Also remember that space info is not 100% accurate, you may buy a 500GB hard drive but you only really get 490 GB
if from the command line you try the df command you can check out
df -h ( this will show you your disk free space in terms computer people call true GB space )
df -H ( this one will give you the measure where a KB is 1000 bytes and not 1024 )
You will see there is quite the difference in the amount of space that shows up on the drive depending on which measure you use
Many times missing space on a hard drive can be found as being lost due to this discrepancy
I would think you could get some fragmentation issues in an ext3 system if they let you use all the space on the drive. Ext3 is pretty good at avoiding that problem, but if they let you use every bit of the hard drive up you likely could start to see problems with the system, since it could never find an empty spot to place your files, and there couldn’t be room to allow them to grow in a contiguous space