> -----Original Message-----
quoted text
> From: Tilo Stritzky [mailto:t.stritzky@teles.de]
> Sent: Tuesday, 23 October 2007 3:07 AM
> To: Edwards, David (JTS)
> Cc: misc@openbsd.org
> Subject: Re: USB Disk problems
>
> On 18/10/07 10:28  Edwards, David  (JTS) wrote:
> > Hi,
> >
> > I'm trying to use USB disks as backup devices and I'm finding that I
> > have problems when I plug in more than two USB drives.  I'm
> using 250G
> > laptop disks powered from the USB cable.
> >
> > Is anyone else seeing this sort of problem?  Would an upgrade to 4.2
> > help?
> >
> FWIW, I have one USB disc where the external power feed goes nowhere.
> If I try to run it on an external feed, a light will come
> up but the drive still feeds on the USB.
>
> Also the power brick you are using could be broken/miswired.
>

Well this seems to have given me the hint that I needed!

I haven't been using external power to the USB disks so far.

The reason is that I originally purchased external 250G
external laptop drives so that the admin dude wouldn't have
to worry about plugging in a power cable as well as the
USB cable.  This seemed like a good idea at the time.

The disks came with an external power cable but it's a second
USB cable with a power plug on the end instead of a mini USB.
During testing, I tried using these power supply cables
on the disks but it didn't seem to have any effect.

After reading your mail, I tried again but this time plugging
the external USB power cable _into_a_different_server_ and it
seems to have worked!  I can now plug in 3 disks reliably.

So it seems that on a HP ProLiant DL360 (G5) using USB powered
external drives, you can only reliably plug in two drives
before you start having power supply problems to the USB disks.
The fix is to provide external power to the third drive
(at least).

<gob smack>
It seems that the whole USB bus including front panel ports,
rear panel ports and all external hubs (even if separately
powered) are electrically one single unit which can only
provide enough power to run two external disks.
</gob smack>

ciao
dave
---
Dave Edwards