I am running Openwrt v18.06.1 on TpLink TD-W8980 v1 and there seems to be a bug in disk usage stats that display from df command. I am using external HDD 500 GB with the router, 2 partitions are on the driver, both formatted as ext4. First partition is for the root and has a capacity of 1 GB, next one is the remainder of the drive.
Everything works as expected but the command shows a little different results:
root@AhmarRouter:~# df -h
Filesystem Size Used Available Use% Mounted on
/dev/root 5.0M 5.0M 0 100% /rom
tmpfs 28.9M 1.2M 27.6M 4% /tmp
/dev/sda1 951.7M 16.0E 937.9M 100% /overlay
overlayfs:/overlay 951.7M 16.0E 937.9M 100% /
tmpfs 512.0K 0 512.0K 0% /dev
/dev/sda2 435.6G 39.0G 373.4G 9% /data
root@AhmarRouter:~# df -m
Filesystem 1M-blocks Used Available Use% Mounted on
/dev/root 5 5 0 100% /rom
tmpfs 29 1 28 4% /tmp
/dev/sda1 952 17592186044375 938 100% /overlay
overlayfs:/overlay 952 17592186044375 938 100% /
tmpfs 1 0 1 0% /dev
/dev/sda2 446100 39933 382355 9% /data
As it shows, the used part shows a very large number in there although that is not possible because of the size of the partition. One more thing is that the LuCI shows 993.11 MBs as free space in Software tab but the free percentage is around 104%. It is definitely inconsistent.