Subject: Re: USB 2.0 support - problems?
To: Wojciech Puchar <>
From: Michael van Elst <>
List: tech-kern
Date: 01/17/2004 15:09:18
On Sat, Jan 17, 2004 at 02:44:27PM +0100, Wojciech Puchar wrote:


> just a question - is this disk capable only of 10-15MB/s or USB driver
> isn't capable to get full speed now?

this is a SP1604 drive (5400rpm, 2MB cache) inside a USB2/Firewire enclosure.
The disk is faster when used directly on an IDE bus. I haven't measured this,
but I would expect about 25-30MB/s for the same test then. A similar
disk (but the 7200rpm,8MB cache model) gets 35-40MByte/s there.

Don't forget that this is a test through the filesystem and the computer
is an EPIA-M 9000 (C3 933MHz) and not your latest Athlon64.

I have used the same drive/enclosure with a firewire connection (to a 
Dell Laptop, 850MHz PIII) and got about 18MByte/s. So the result with
USB2 is close to what I expected.

> (or maybe this 480Mbit/s is just pure theory)

This is just theory. There is overhead, there is reserved bandwidth
and then there is overhead. Under ideal conditions (i.e. a Windows
system) the best you will see is about half of the theoretical value
(~ 30MByte/s).

                                Michael van Elst
                                "A potential Snark may lurk in every tree."