I don't think that USB would have that type of limitation, unless there was a driver issue preventing it. Hardware, I would say 'no'.
Hi, I inherited responsibility for a Poweredge 2900 server last year. Recently I was asked to mount an NTFS 5TB external USB drive. This failed with the following message: $ mount /mnt/external_usb_3Failed to read last sector (1220940596): Invalid argumentHINTS: Either the volume is a RAID/LDM but it wasn't setup yet, or it was not setup correctly (e.g. by not using mdadm --build ...), or a wrong device is tried to be mounted, or the partition table is corrupt (partition is smaller than NTFS), or the NTFS boot sector is corrupt (NTFS size is not valid).Failed to mount '/dev/sdf1': Invalid argumentThe device '/dev/sdf1' doesn't have a valid NTFS.Maybe you selected the wrong device? Or the whole disk instead of apartition (e.g. /dev/hda, not /dev/hda1)? Or the other way around? I know the Poweredge 2900 has an internal HDD limit of 2TB due to the PERC5/i controller. Is this also true for external USB drives? Or is it another HW or OS limitation? I was reading the documentation and could not find (or over-looked) the answer. Is there any way to mount a drive this size by reformatting/repartitioning? Thanks, Brendan 
Poweredge 2900 - Maximum external USB drive size