USB 2.0: realistic transfer speeds?

[Robert Huff]

	I'm testing a possible new backup arrangement, involving an
external hard disk connected by USB 2.0.  Now the quoted 60
mbyte/sec is obviously the "maximum theoretical rate"; however, it
seemed reasonable to get 30, 20 or even 15.
	Instead it's having trouble breaking the 10 barrier, and some
operations are never make it past 6.  (Which is better than the ~1 
from a USB 1.1 connection, but still ....)
	So - for those who have experience with bulk transfers across
USB or good theoretical knowledge: what's a reasonable number?
	(Background information: this is driven by the stock dump that
comes with:

	FreeBSD 7.0-CURRENT #0: Tue Nov 14 17:38:15 EST 2006

	and my hardware list is appended.  (I'm curious more than
concerned about the [GIANT-LOCK] and "Uninitialized Transport 5:0?".))



					Robert Huff



Jan 14 10:07:55  kernel: ehci0: <ALi M5239 USB 2.0 controller> mem 0xf0000000-0xf00000ff irq 15 at device 10.3 on pci0
Jan 14 10:07:55  kernel: ehci0: [GIANT-LOCKED]
Jan 14 10:07:55  kernel: usb3: <ALi M5239 USB 2.0 controller> on ehci0
Jan 14 10:07:55  kernel: umass0: <Addonics Addonics USB Drive, class 0/0, rev 2.00/0.15, addr 2> on uhub3
Jan 14 10:07:55  kernel: (probe15:umass-sim0:0:0:0): Uninitialized Transport 5:0?
Jan 14 10:07:55  kernel: da2 at umass-sim0 bus 0 target 0 lun 0
Jan 14 10:07:55  kernel: da2 at umass-sim0 bus 0 target 0 lun 0
Jan 14 10:07:55  kernel: da2: <Maxtor 6 L100P0 0000> Fixed Direct Access SCSI-0 device 
Jan 14 10:07:55  kernel: da2: 40.000MB/s transfers
Jan 14 10:07:55  kernel: da2: 95611MB (195813072 512 byte sectors: 255H 63S/T 12188C)