Mailinglist Archive: opensuse (6210 mails)

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Re: [SLE] unplugging USB hard disks
  • From: Randall R Schulz <rschulz@xxxxxxxxx>
  • Date: Sat, 29 Oct 2005 07:23:16 -0700
  • Message-id: <200510290723.16385.rschulz@xxxxxxxxx>

On Saturday 29 October 2005 02:08, Kevanf1 wrote:
> On 29/10/05, Bryan Tyson <bryantyson@xxxxxxxxxxxxx> wrote:
> > On Friday 28 October 2005 17:01, Kevanf1 wrote:
> > > I know that you
> > > couldn't simply unplug old style serial or parallel port drives
> > > etc because of the risk of burning the port out, this shouldn't
> > > happen with USB. Should it?
> >
> > No, the automounting is in sync mode so you should be able to
> > unplug any time there is no activity. I have never heard of a usb
> > port "burning out."
> >
> > Bryan
> Ok, I'm with you guys so far :-) Now, my next question is how do you
> know when data has finished its transfer to the USB device? I know
> that a lot of USB devices have a light that wither blinks on and off
> or stays on during data transfer. But there must be a another way of
> registering the transfer - it usually opens a window if you are in
> GUI mode but this is not the case in command prompt mode. What I'm
> getting at is the same as with a car. You should never rely on the
> oil warning light to come on and tell you that you are low on oil
> because the light/bulb may have blown or be otherwise defective. The
> same goes for this tell tale light on the USB device. Or am I now
> worrying for no reason?

For god's sake, drop the automotive analogies, OK?

Once again, ...

There are two parts to synchronous file system writing. One is that the
kernel does not hold on to dirty buffers--it always flushes them to the
device immediately upon receipt of new data from the user-level

The other is that it does not return control from the write system call
that sent data to the device until the write is complete. If you're
using simple GUI commands that perform some operation and return (as
opposed to interactive commands which _might_ be multi-threaded, though
many are not), then by the time you see the prompt after issuing the
command that sends data to the USB-attached device, all the I/O is
complete and the device may be disconnected.

And LEDs have a very, very, very long lifetime. You'll have long
abandoned your USB device as obsolete for one reason or another (or
because it has failed, stopped on or dropped in the toilet) before the
indicator lights stop working.

> ..
> Kevan Farmer

Randall Schulz

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