Very slow USB 3.0 data transfer on Ubuntu 11.10

[Christopher Beynon]

Computer: ZOTAC ZBOX AD02 (AMD E-350 APU Platform) with two USB 3.0 ports.
Ubuntu 11.10.
Two external harddisks (FAT 32 resp. NTFS) in USB 3.0 enclosures.
When copying between to two harddisks, I get only transfer rates of
about 6 MB/s.
With Windows 7 with the same setup (dual boot) I get transfer rates of
about 80 MB/s.

Any suggestions?

Regards
Christopher