Please I want to know if it's possible to extract the MicroSD when It's unused and unmounted and the Udoox86 is on ? (hot extraction, in italian "estrazione a caldo")
Sure, all depends on the operating system. This is not a function of the hardware, it's no different than any other microSD card slot on an SBC. It matters how the OS is handling the drive and logical function.
Then Maurice you think that's better to remove the MicroSD when UdooX86 is off if you are not sure of the OS "behaviour" ?
@stecolumna A SD card that is not used and not mounted will never ever give problems, for the OS it is as if it is not in the SD card slot at all. The only way a SD card (or any removable medium) can give problems if you have mounted it and the OS hasn't flushed all changes to it. That's what the unmount (or eject) does, give the OS the opportunity to write any pending changes to it. If you mount the SD card in 'sync' mode you are not even likely to have a problem with removing it without unmounting it, given that there is no active write operation of course. It will impact performance though.