im just posting this for posterity because it was a pain to google for a clear answer, & maybe this will help someone else in the future.
i was trying to figure out why a 4tb external ssd i bought would be discoverable on my pc but not my phone or tablet.
some searching told me that it was either incompatible file system, or lack of power.
i bought a powered hub & was able to discover the 4tb ssd (formatted as ntfs) on my tablet. without the hub, it would cause constant restarting of the tablet due to power draw overload.
i also had a new 1tb sd card that i wanted to clone onto, & discovered that while the tablet can read an external ntfs drive, the sd card formatted to ntfs was deemed unacceptable & prompts a reformat dialogue, inviting a change to exfat.
i found that new sd cards inserted into the tablet first were automatically formatted to exfat.
my pc had no problem reading either exfat or ntfs sd card as flash storage.
i also found that new sd cards come with an unallocated partition proportionate to the drive size, i.e. 1tb had a 64mb unallocated partition, 512gb had a 32mb unallocated partition. apparently this is meant as a sort of ram or temp storage for the card in the event that the main partition is completely filled.
