root@OpenWrt:~# ubinfo -a
UBI version: 1
Count of UBI devices: 1
UBI control device major/minor: 10:126
Present UBI devices: ubi0
ubi0
Volumes count: 2
Logical eraseblock size: 15872 bytes, 15.5 KiB
Total amount of logical eraseblocks: 3840 (60948480 bytes, 58.1 MiB)
Amount of available logical eraseblocks: 0 (0 bytes)
Maximum count of volumes 92
Count of bad physical eraseblocks: 0
Count of reserved physical eraseblocks: 80
Current maximum erase counter value: 4
Minimum input/output unit size: 512 bytes
Character device major/minor: 251:0
Present volumes: 0, 1
Volume ID: 0 (on ubi0)
Type: dynamic
Alignment: 1
Size: 787 LEBs (12491264 bytes, 11.9 MiB)
State: OK
Name: rootfs
Character device major/minor: 251:1
-----------------------------------
Volume ID: 1 (on ubi0)
Type: dynamic
Alignment: 1
Size: 2969 LEBs (47123968 bytes, 44.9 MiB)
State: OK
Name: rootfs_data
Character device major/minor: 251:2
root@OpenWrt:~# df -h
Filesystem Size Used Available Use% Mounted on
/dev/root 12.0M 12.0M 0 100% /rom
tmpfs 58.9M 2.5M 56.4M 4% /tmp
/dev/ubi0_1 32.9M 2.9M 27.9M 9% /overlay
overlayfs:/overlay 32.9M 2.9M 27.9M 9% /
tmpfs 512.0K 0 512.0K 0% /dev
root@OpenWrt:~#
UBI0:1 partition is 44.9MB big, but df shows that ubi0_1 is just 32.9MB big. 12MB space has gone, and that is close to UBI0:0 which is squashfs rootfs.
Where do these space go? Is it a bug?
I tried Chaos Calmer and Snapshot branch, both of them have this problem.