Few file systems are quite as robust as the ext series. Part of this robustness comes from the fact that newer versions use journals, which can also be disabled for use on USB NAND drives. Some support also comes from the fact that these systems reserve a portion of the free space so that system services can always run. This allows fsck to run under any circumstance, and it provides empty space for the lost+found directory each of these disks must have.
If you’re using an external storage volume, however, you may not need very much space reserved. Most modern Linux distributions have the file system creation commands set to reserve 5% on all new partitions, which is probably necessary on your boot drive, but not necessary on any other partition. External drives seldom need to reserve this much space. You can reclaim some of this space with the tune2fs command. It should work for newer ext4 partitions as well in spite of the name of the command.
Method 1: Altering the Amount of Reserved Space
Make sure that the partition in question is unmounted before you proceed. From the Linux CLI prompt, type the following command:
tune2fs -m 0.2 /dev/sdd1
If you don’t have root access, then you’ll need to put sudo in front of it. Change the value after -m to whatever percentage you want to set the reserved space to. While some people recommend 0, this is inadvisable since it provides little space for fsck to run if there were an error. You could also theoretically increase the amount of space if you were working with server drives. Change the partition identifier to whatever device file represents it.
Method 2: Counting Reserved Blocks
If you want to make sure that the number of reserved blocks changed, then simply issue the following at the Linux CLI prompt while changing the device file to whatever points to the partition in question:
tune2fs -l /dev/sdd1
Look for a field called “Reserved block count,” which will report the number for that partition only.