Write data to SD Card on board UniElec U7621-06 will cause file system broken

Installing and Using OpenWrt
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I have two boards of "UniElec U7621-06".

I am testing the SD card read and write. But meet problems.

  1. mkfs.ext4 /dev/mmcblk0p1 successed, but execute "mount /dev/mmcblk0p1 /mnt" then get Invalid Param error.
  2. I format SD at first on general Linux like ubuntu, and plug it on board, it mounts successed, after I write some data to the /mnt dictionary, like mkdir or touch an empty file, then umount and mount again, got invalid param error too.

And I plug the SD card on general Linux, it says the file system is broken, the system can't recognize the fs type.
I can almostly get the conclusion that writing data to the SD card on board will cause its file system broken.

I followed the official manual:

  1. using the official image, http://downloads.openwrt.org/releases/19.07.2/targets/ramips/mt7621/openwrt-19.07.2-ramips-mt7621-unielec_u7621-06-256m-16m-squashfs-sysupgrade.bin
  2. Default image doesn't support ext4, so I follows the direct of "Extroot configuration" and use opkg to install the packages.
    "opkg update && opkg install block-mount kmod-fs-ext4 kmod-usb-storage e2fsprogs kmod-usb-ohci kmod-usb-uhci fdisk"

BTW, if I plug the USB disk to the usb port on the board, it causes rebooting.

Seems like a power supply problem? Could any one can help me. Thanks.

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That would be a good explanation.
For the SD card, I would try another one to rule out the faulty SD variant.

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I tested several SD cards, they are kingston 8G , SanDisk 16G, OV 8G(which I never heard).
It is strange that only SanDisk 16G is ok, and another two models are all getting error.

It seems the SD cards incompatibility problem.

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As I mentioned before that plugging flash disk to USB port will cause system rebooting, which is my fault.
In order to test SD card, I unscrew the screws on board for convenience, this makes the board get loose when plugging flash disk and cause rebooting I guess.

After I make the board fixed and no rebooting occurs.

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