How to save disk space by changing the reserved blocks for Ext-filesystems
Published: Thursday, May 28, 2020
By default the Extended-filesystem, more known as Ext2/4, reserves 5% of the filesystem blocks on the filesystem for privileged processes. It’s done to avoid filesystem fragmentation and to allow system daemons to continue to function correctly after non-privileged processes are prevented from writing to the filesystem due to a full filesystem.
It’s a great feature for system critical filesystems, but if you have a storage disk you usually don’t need that feature at all. And if you have a very large system disk you could probably lower the value a bit, but that’s for you to decide.
An example with my storage disk
I have turned off the reserved blocks on my storage disk and as you can see below it does make a noticeable difference on a larger filesystem.
$ df -h Filesystem Size Used Avail Use% Mounted on [...] /dev/sdb1 3.6T 1.9T 1.6T 55% /mnt/hdd0
$ df -h Filesystem Size Used Avail Use% Mounted on [...] /dev/sdb1 3.6T 1.9T 1.8T 52% /mnt/hdd0
Start by checking the amount of reserved block count you have on the disk:
# tune2fs -l /dev/sdb1 | grep 'reserved block count' Reserved block count: 48837696
If you don’t know what your device names is you can list them with the command
fdisk -l as a privileged user. In my case the device name was
To change the value we are going to use the tool
tune2fs. In this example I changed the value to
0 (zero) with the flag
# tune2fs -m0 /dev/sdb1 tune2fs 1.45.5 (07-Jan-2020 Setting reserved blocks percentage to 0% (0 blocks)
You can then double check to see if it worked:
# tune2fs -l /dev/sdb1 | grep 'reserved block count' Reserved block count: 0
If you want to leave feedback you can do so by either sending me a message via e-mail or by commenting on my post for this article on the fediverse.