Is there a way to make ext-filesystems use less space for themselves in Linux?

By default, ext2 and its successors reserve 5% of the filesystem for use by the root user. This reduces fragmentation, and makes it less likely that the administrator or any root-owned daemons will be left with no space to work in.

These reserved blocks prevent programs not running as root from filling your disk. Whether these considerations justify the loss of capacity depends on what the filesystem is used for.

The 5% amount was set in the 1980s when disks were much smaller, but was just left as-is. Nowadays 1% is probably enough for system stability.

The reservation can be changed using the -m option of the tune2fs command:

tune2fs -m 0 /dev/sda1

This will set the reserved blocks percentage to 0% (0 blocks).

To get the current value (among others), use the command :

tune2fs -l <device> 

Another point which has not been talked about yet is the number of inodes you reserve on your file system.

Per default, mkfs creates a number of inodes which should make it possible to put a whole lot of very small files into your file system. If you know that the files will be very big and you will only put a small number of files on the FS, you can reduce the number of inodes.

Take care! This number (resp. the ratio between space and number of inodes) can only be set at the file system creation time. Even when extending the FS, the ratio remains the same.

if the data you intend to store on it is compressible, btrfs mounted with compress=zstd (or compress-force=zstd) would probbaly use significantly less disk space than ext*

• this will make btrfs transparently compress your data before writing it to disk, and transparently decompress it when reading it back. also, ext4 pre-allocate all inodes at filesystem creation, btrfs creates them as needed, i guess that might save some space too.