USB physical ports

Lowell Gilbert freebsd-questions-local at
Fri Sep 11 13:28:16 UTC 2015

Ernie Luzar <luzar722 at> writes:

> /root/bin >dd if=/dev/da0 of=/dev/null bs=1M count=400
> 400+0 records in
> 400+0 records out
> 419430400 bytes transferred in 22.415176 secs (18711894 bytes/sec)
> If 20Mbps is the max rate Freebsd can do, then 18.7Mbps is a good rate.

You're confusing bits with bytes. 19 megabytes per second is (with
overhead) over 250 megabits per second, which is a bit over half of the
theoretical max for USB 2.0, but perfectly respectable for inexpensive
flash drives.

> But the real question is why is Freebsd USB rates capped at 20Mbps
> when the hardware says it's capable of 480Mbps?

The hardware is capable of transfers at 480 megabits per second, but
that doesn't mean that the flash can physically read data that quickly.

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