Why USB harddrive is so slow under FreeBSD?

[Frederique Rijsdijk]

Yuri wrote:
> I have FreeBSD-71 running with USB controller:
> uhci0: <VIA 83C572 USB controller> port 0xa800-0xa81f irq 21 at device 
> 16.0 on pci0
> 
> I connected to it Toshiba USB hard drive HDDR500E03X:
> umass0: <Toshiba External USB HDD, class 0/0, rev 2.00/1.03, addr 2> on 
> uhub4
> da0: <Toshiba External USB HDD 1.03> Fixed Direct Access SCSI-4 device
> 
> When I try to copy data with 'dd if=/dev/da0s1 of=/dev/null count=10000' 
> it only achieves has 0.65MB/s transfer speed.
> 

I get around the same speeds if I do it that way.

But if I add 'bs=1m', speeds go up to 27MB/sec.