What is the largest capacity USB flash drive that can be used in a 4RE?
The 4RE comes with a 16GB USB flash drive, and WatchGuard has 32GB USB flash drives available. Larger-capacity USB flash drives can be used, but they must be formatted as FAT32.
Windows will format a USB flash drive as FAT32 up to a capacity of 32GB. There are utilities available online that will format larger-capacity USB flash drives as FAT32.