mkfs.ext4 -m -T options

Solution 1:

Execute as root:

dumpe2fs | less

There is a line Reserved block count, which tells how many blocks are reserved. Dividing Reserved block count by Block count gets you the percentage of reserved blocks.

The -T option selects which configuration to use from /etc/mke2fs.conf. The main setting that changes is the inode_ratio, which tells how much filesystem space one inode covers.

To get back to that number, one needs to do following steps:

1. Get block device size by running df -k /path/to/filesystem.
2. Take the value from 1K-blocks column and multiply by 1024.
3. Run dumpe2fs /path/to/filesystem | grep "Inode count" to get the number of inodes on the filesystem.
4. Divide the value from step 2 by the value from step 3.

The result is a number close to 4194304, which is the inode_ratio specified for largefile4 in mke2fs.conf, if the filesystem was created with largefile4 option.