You can attach external hard drives using the two USB 3.0 ports, which are compatible with all external hard drives and USB flash drives. Note that unless drives are adopted as internal storage, they can't be used for app or game storage. Simply plug the USB storage device of your choice into the port for automatic functionality. No additional formatting or setup is required. Your SHIELD TV's USB 3.0 interface is compatible with the FAT32, exFAT, and HFS+ file systems. SHIELD TV does not support the NTFS file system.
To access the USB storage drive on your SHIELD TV, go to Settings > Device > Storage & reset and scroll down to USB Storage
FAT32 (32 GB or less) - SHIELD TV supports the FAT32 data format. Most drives that are 32 GB or less are already formatted as FAT32. If the storage drive is not formatted, format it to FAT32, using your PC or Mac computer. The limitation of using drives of this capacity is that your SHIELD TV will be unable to process files that are more than 4 GB in size.
exFAT (64 GB or more) - SHIELD TV supports the exFAT data format. Storage drives that are 64 GB and above come pre-formatted as exFAT. This newer data format is able to process files that are more than 4 GB in size.