With sbitx, it is worth booting from an external USB 3 because there is a speed difference.
Here, the RPi4 also boots from the uSD card on the pcb, while the uSD has a speed of 30 MB/s, while the external USB 3 speed (depending on the quality of the stick) reaches a 10x increase.
I recommend replacing the internal uSD card because I think there is not that much gain with the external USB.
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Gyula HA3HZ
HA3HZ