Re: rescan scsi

Rogier Wolff (
Sat, 21 Jun 1997 11:10:04 +0200 (MET DST) ;The Doctor What wrote:
> I have a question....why do people say NOT to add scsi devices on the
> fly to a system? I thought that was (inpart) the point of SCSI?
> The only things I can think of is:
> 1) The device generates a "startup" message that does evil things to
> the SCSI card. (Which doesn't make sense, since I always turn off
> external scsi devices if I'm not using them for an extended period of time).
> 2) There is a chance of an electrical discharge that frys hardware....

You are running more than a WATT of power to the terminator.
Disconnecting that might cause inductance to generate voltages that
are much too high for computer components.

As the disclaimer in the kernel says: You're not supposed to hot-swap
devices. You are maybe allowed to turn off devices that are not used
for longer periods. I have an external ROM burner and a scanner, and
those only get turned on whenever I use them.

There are also systems that have special hot-swap slots (RAID systems
come to mind).... These can be safely hot-swapped as the designers
assume responsibiltiy that they took care of all issues related to
the hot swapping....

In practise you can hot-swap SCSI devices with just a small chance of
blowing up stuff. At the company a friend works for, they fried an
SGI's scsi bus, external CDROM drive, and the internal DAT drive by
hotswapping the CDROM. I occasionally hot swap my equipment too.
It usually survives.... :-)