A while back I bought an external hard drive for backing up my flacs and my photos.



Recently it started to fill up.

This was, of course, a bad thing.

I looked at how much space I had left on it:





Filesystem Size Used Avail Use% Mounted on

/dev/external 276G 259G 2.5G 100% /mnt/external



So, I had 2.5GB free. But hold on, the maths doesn’t make sense.



I have a 276GB drive, with 2.5GB free, yet I’ve only used 259GB.



I’m missing 14.5GB!

I did some googling and found out the following:



The most likely reason is reserved space. When an ext2/3 filesystem is formated by default 5% is reserved for root. Reserved space is supposed to reduce fragementation and allow root to login in case the filesystem becomes 100% used. You can use tune2fs to reduce the amount of reserved space.

So, ext2/3 reserves 5% of space, which on my drive is 13.8GB – well, that’s close enough to 14.5GB, so that explains that mystery.



The next questions was; can I and should I reduce that amount of reserved space?

More googling:



The reserved blocks are there for root’s use. The reason being that the system gets really narky if you completely run out of room on / (specifically /var, or /tmp, I think). Programs won’t start, wierd errors will pop up, that sort of thing. With some room reserved for root, you can at least be sure to be able to run the really important programs, like sudo and rm . So, in short, if the drive doesn’t contain /var or /tmp, then there’s not much point in having space reserved for root.

So, some poster on some Internet forum says it’s probably OK to do away with that reserved space.



That’s usually good enough for me, but I figured this time I’ll play it safe and reduce it to 1%.



So I unmounted the drive and ran the following command: tune2fs -m 1 /dev/external

I re-mounted and voila, 11.5GB appeared out of nowhere!





Filesystem Size Used Avail Use% Mounted on

/dev/external 276G 259G 14G 95% /mnt/external



I’ve now run this on my other non-booting partitions.



All seems fine so far.



I’ll leave my system partition at 5% I think though, just to be safe.