External usb HDD disconnects, system gets messed up

[Bernd Walter]

On Fri, Dec 03, 2010 at 11:01:30AM +0000, Marcin Wisnicki wrote:
> On Fri, 03 Dec 2010 10:06:58 +0100, Hans Petter Selasky wrote:
> 
> > On Friday 03 December 2010 02:37:43 Marcin Wisnicki wrote:
> >> On Fri, 26 Nov 2010 08:17:47 +0100, Hans Petter Selasky wrote:
> >> > I think that the USB part of your USB disk has died or there has been
> >> > a firmware crash. Other OS'es will perform a complete device reset in
> >> > this situation and sometimes that help, but still that is hiding a
> >> > problem about the device. We don't do that on FreeBSD, and that might
> >> > be the reason it does not recover.
> >> 
> >> Then print a warning. A lot of self-powered 2.5 disks I've used had the
> >> same problem.
> >> 
> >> Also, would it be possible to somehow keep the kernel device if
> >> physical device reappears within few seconds (with i/o temporarily
> >> frozen) such that existing mount points keep working ?
> > 
> > Hi,
> > 
> > It would require some patching. It is not impossible to do, but I think
> > that it should not be required. If a disk drive does not work properly
> > with FreeBSD then you should be careful using it to store your data. It
> > might be that the vendor of your USB HDD has only tested using one OS.
> > It might be that OS is not FreeBSD.
> 
> I'm willing to bet that no vendor does testing with FreeBSD ;)
> 
> > 
> > Please try to get support from your USB HDD manufacturer. I'm pretty
> > sure that it is not a problem with FreeBSD USB or FreeBSD CAM layer.
> 
> Indeed, it happens in any OS. But Windows handles it gracefully, would be 
> nice if FreeBSD did too.
> 
> > 
> > I've been using a USB HDD enclosure for the last couple of years now
> > without any problems at all, even though the USB connector is starting
> > to get broken.
> > 
> 
> Unfortunately it is impossible to know it before buying. Typical consumer 
> does not use external hdd for more than couple of hours at a time so there 
> are no reviews or complaints about it. You won't get your money returned 
> either if it's just "sometimes a ding-dong sound is played if drive is 
> used for more than 20 hours" which is all that happens in Windows.

HDD enclosures are heavy enough to leave marks if thrown at vendors heads.
If people don't complain about crappy devices nothing will ever change.
However - there is another possible problem case: ground loops.
Some devices are oversensitive to them.
Your PC is typically grounded and sometimes devices are as well or
devices are connected to grounded (e.g. RS232 converters) devices.
If this happens with audio wiring people usually notice the noise and
try to avoid, but with digital signals it only gets noticed if it's
too late already - unfortunately USB has no way to measure signal
quality by itself.

-- 
B.Walter <bernd at bwct.de> http://www.bwct.de
Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.