why does ax86u has only 47mb jffs when it has 256MB flash?

[2ig2ag]

RT-AX86U-8D08# df -h
Filesystem                Size      Used Available Use% Mounted on
ubi:rootfs_ubifs         77.7M     75.7M      2.1M  97% /
devtmpfs                456.0M         0    456.0M   0% /dev
tmpfs                   456.1M    720.0K    455.4M   0% /var
tmpfs                   456.1M      1.1M    454.9M   0% /tmp/mnt
ubi1:data                 4.5M     64.0K      4.2M   1% /data
tmpfs                   456.1M      1.1M    454.9M   0% /tmp/mnt
tmpfs                   456.1M      1.1M    454.9M   0% /tmp
/dev/mtdblock9           47.0M     25.5M     21.5M  54% /jffs

The root has 77.7M and jffs has 47.0M. That's 124.7 MB in total. It's far from "256 MB Flash" in Asus's tech specs.
What gives?

 

[ColinTaylor]

The flash memory is used for more than the visible filesystems. But most of the "missing" space is used to hold a backup copy of the entire firmware image. So should the current firmware get corrupted it's possible to recover from the previous version.

 

[RMerlin]

96 MB for the first firmware partition.
96 MB for the second firmware partition
Some portions for bootloader, crashlog storage, system data, etc...
What's left (around 48 MB) is for JFFS.