Reclaiming ext3 disk space

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.

5 thoughts on “Reclaiming ext3 disk space”

  1. Hi!
    Absolutely agree that systems have plenty of odd ruses! Unnecessary ones, I should say. I reduced the reserved space to 1% like you did, but before this I found out that the system starts a lot of processes that slow down the work of the computer but these one are not of great need! I switched them off and now every action takes twice less time than before, especially when I was using FTP editor – I had my ICQ and Word dying because of the overburden processor. Now I am turning the world upside down at one stroke 🙂

  2. Thanks for that extremely concise solution!
    I just thought I’d try out ext3 on one of my big scratch disks (previously Fat32 for compatability reasons) and saw a huge cunk of reserved space missing. I thought it must have been the journaling, but your explanation made me realize it was non-vital for non-booting disks.

    And yes I know how narky the system gets about running out of space on / … that’s Why I was juggling scratch disks in the first case 🙂


    I just formated my 500GB (My Book) drive to ext3 using “Partition Editor – GParted 0.3.3”.

    When I bought the drive, it came as a fat32 drive and had some google and other files on it.

    first I tried using QTparted (took 5 seconds) that did format but later showed up as error, so I used GParted (took 6.5 minutes) and it went all well and I mounted the drive now as an ext3 drive.


    1. The drive in size shows as 465.76GB, but it shows 7.50GB used and 458.26GB unused, how can that be, I just formated the whole drive and have put nothing on it, so what is using the 7.50 GB?

  4. @mozart

    The reason you are seeing 7.50GB used is due to the reserved space for root on the filesystem. Read the first post to resolve.


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