A tablet or Android running smart phones usually doesn’t support external hard drive. They support USD sticks up to 64GB or even maybe 128GB but it doesn’t support hard disk and definitely 1TG is not possible at all, because these devices are not yet designed to support such large storage media. But if a new introduced tablet claim this functionality then the following points should be considered:
1. The tablet like a computer must have USB on the go support.
2. The external hard drive must contain an alternative power source as the tablet can’t able to power the disk via USB.
3. Only some limited file system are accepted, like FAT, FAT16 and FAT32 (as Android usually support these file system).