You do not need an SSD boot device, but we discourage using a spinner or a USB stick.
We do not recommend installing TrueNAS on a single diskor striped pool unless you have a good reason to do so. You can install and run TrueNAS without any data devices, but we strongly discourage it.
i’m not calling you out or anything, i also use a single boot drive, and some mirror boot drive. i use both types for different nas depending what i have available at the time during setup.
but officially that is the recommendation. not just them, even other places may say something similar.
this is an interesting case study what happens and whether mirror boot pool is all it’s cracked up to be or not. maybe there is much more to it than just that, but interesting nevertheless
i think eric summed it up nicely
but back to the original question
Using USB Thumb drive to run as boot volume Truenas Scale
No. you definitely shouldn’t use usb flash sticks for that. Usb external enclosures e.g. m.2 nvme ssds which is what i use for a truenas boot drive are fine
Avoid using USB-connected hard disks for primary storage with TrueNAS. You can use USB Hard Disks for very basic backups in a pinch. While TrueNAS does not automate this process, you can connect a USB HDD, replicate at the command line, and then take it off-site for safekeeping.
https://www.reddit.com/r/truenas/comments/t4owwl/can_i_run_truenas_core_off_usb_sticks/