What Do I Do If the Combined Used and Available Disk Space Is Not the Same as the Total Disk Space in an EXT4 File System?

Symptom

When df -m is used to check disk space, the sum of the used disk space and available disk space is not equal to the total disk space, for example, in the following picture, where 29955 is more than 12366 + 16991.

Figure 1 Using df -m to check the disk space

Possible Cause

By default, an ext4 file system reserves some space (usually 5%) for system users so that they can still run key commands when the disk is "full". You can use tune2fs -l /xx/xx to query the reserved space of an ext4 file system. In the following example, 156,712 blocks are reserved.

Figure 2 Querying reserved disk space

Solution

1. It is normal for some disk space to be reserved for a system partition. You are not advised to change it.

2. For data partitions that can accept the risk of a full disk, you can reduce their reserved space by running tune2fs -m x /xx/xx. For example, run tune2fs -m 2 /dev/mapper/hce-home to set the percentage of reserved space for the home partition to 2%.