Why my device only have 8.9M flash useable?

My device is Xiaomi 4A 100M. It have 16M flash.

Takes some to install openwrt.

  • 16 MB total flash size

Depending on how you look at it, this leaves you with one of these calculations:

  • 12.928 MB - 5.750 MB = 7.178 MB available for the overlay ~= free space
  • 12.928 MB - 2.107 MB = 10.821 MB available for rootfs+overlays ~= space not used 'invisibly' by the kernel

The calculations do not consider erase block borders (64 KB) and the padding needed between them (up to 192 KB in the worst case) or filesystem overhead for the overlay (jffs2), so the actual free space is reduced by those.

If you need/ want more than that, you will have to look into better hardware.

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16 MB - 12.928 MB = 3.072 MB, What it used for ?

Do a cat /proc/mtd and find out.

Bootloader, wifi calibration data, etc.

Generally, OpenWrt tries to avoid modifying the existing partition structure and also bootloader, so the available size (for kernel, rootfs, user data) is largely determined by the OEM manufacturer.

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Thank you all.

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