EXT4 file system disable reserved blocks

Recently add a 4TB HDD as secondary data drive on my Lubuntu 22.04 LTS. It use ext4 as default file system and I notice the free disk space does not add up compare to the used disk space.

user1@user1-pc:~$ df -h

Filesystem      Size  Used Avail Use% Mounted on
tmpfs           3.2G  1.6M  3.2G   1% /run
/dev/sda2       439G  156G  261G  38% /
tmpfs            16G     0   16G   0% /dev/shm
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs            16G     0   16G   0% /run/qemu
tmpfs            16G     0   16G   0% /tmp
/dev/sda1       300M  6.0M  294M   3% /boot/efi
/dev/sdb1       3.6T  2.6T  882G  75% /mnt/sdb1
tmpfs           3.2G   84K  3.2G   1% /run/user/1000

Upon further checking, I found out ext4 file system will reserve 5% disk space for root as emergency. Since the drive is for data storage, there is no need to reserve the disk space.

user1@user1-pc:~$ sudo tune2fs -l /dev/sdb1 | egrep "Block size:|Reserved block count"
Reserved block count:     48837683
Block size:               4096

Use tune2fs utility to set the reserved blocks to 1% or 0% to disable it.

user1@user1-pc:~$ sudo tune2fs -m 1 /dev/sdb1
tune2fs 1.46.5 (30-Dec-2021)
Setting reserved blocks percentage to 1% (9767536 blocks)

user1@user1-pc:~$ sudo tune2fs -l /dev/sdb1 | egrep "Block size:|Reserved block count"
Reserved block count:     9767536
Block size:               4096

user1@user1-pc:~$ df -h
Filesystem      Size  Used Avail Use% Mounted on
tmpfs           3.2G  1.6M  3.2G   1% /run
/dev/sda2       439G  156G  261G  38% /
tmpfs            16G     0   16G   0% /dev/shm
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs            16G     0   16G   0% /run/qemu
tmpfs            16G     0   16G   0% /tmp
/dev/sda1       300M  6.0M  294M   3% /boot/efi
/dev/sdb1       3.6T  2.6T  1.1T  72% /mnt/sdb1
tmpfs           3.2G   84K  3.2G   1% /run/user/1000