You are writing commands in the device firmware shell. These commands must be written in the uboot shell.
Below you are writing it in the uboot shell, which is the correct place.
For some reason the stock bootloader is unable to detect the USB drives you are using. I don't know why, but some people did have issues like that.
You have to transfer the files with tftp, it's a bit more annoying, I'll post instructions below.
If you install successfully with the following instructions I'll update the wiki with this additional method.
Prepare the tftp server and the files you want to transfer as described here: https://openwrt.org/docs/guide-user/troubleshooting/tftpserver?s[]=tftp#tftp_server_on_windows
Set your PC's ethernet port to have fixed IP address 192.168.1.10 and connect it with an ethernet cable to the NSA310 ethernet port.
boot the NSA310 and reach the uboot (bootloader) console by pressing a key as soon as you see the prompt.
You should see
NSA310>>
Now write
setenv ipaddr 192.168.1.1
setenv serverip 192.168.1.10
Then you can begin the file transfer with
tftp 0x1000000 u-boot.kwb
It should show a progress bar and will tell you if the transfer was successful.
If it's good, then you can proceed with the other instructions, to install the OpenWrt uboot
nand erase 0x0 0x100000
nand write 0x1000000 0x00000 0x100000
reset
Then write your device's mac address as written in the sticker under the NSA310 ( the AB:CD:EF:00:00:00 you see below is an example MAC address, please write your device's MAC in the terminal)
setenv ethaddr AB:CD:EF:00:00:00
saveenv
Then, you can try with normal instructions as you have just installed a different uboot, that should be able to read from USB.
usb reset
fatload usb 0 0x2000000 nsa310.bin
If it fails again, you must use tftp again to load OpenWrt firmware too.
write
setenv ipaddr 192.168.1.1
setenv serverip 192.168.1.10
tftp 0x2000000 nsa310.bin
and then proceed with
nand erase.part ubi
nand write 0x2000000 ubi 0x600000
reset
And OpenWrt should be installed.