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SubjectRe: The advantage of modules?
Date
Michael Meissner writes:
> Quoting from drivers/scsi/scsi.c:
>
> /*
> * Usage: echo "scsi add-single-device 0 1 2 3" >/proc/scsi/scsi
> * with "0 1 2 3" replaced by your "Host Channel Id Lun".
> * Consider this feature BETA.
> * CAUTION: This is not for hotplugging your peripherals. As
> * SCSI was not designed for this you could damage your
> * hardware !
> * However perhaps it is legal to switch on an
> * already connected device. It is perhaps not
> * guaranteed this device doesn't corrupt an ongoing data transfer.
> */
>
> so my take is unless you explicitly use hotplug devices (I wasn't), that
> it is much safer to unload the driver, unattach/attach scsi devices, and
> then reload the driver (which will scan the scsi bus for devices), which
> you need modules for.

I don't believe that is what it's trying to say. There have been instances
in the past where unplugging a SCSI device from a powered on SCSI bus can
result in blown terminator power fuses and the like. Whether this still
applies today, I don't know (are active terminators better or worse than
passive when it comes to this type of thing?) However, what I do know is
the following, and I learnt it the hard way:

I once had a machine and other stuff on a 4-way mains connector block
that has been used for many years. Unknown to me, the earth wire
had become intermittent. I was just about to connect another peripheral
which was directly connected to the wall socket to this computer, and
I happened to touch the connector body on both the peripheral and the
computer. I now know what a shock of >120V feels like.

Now, imagine what would happen if you connect a SCSI device, where this
condition exists, and the first thing that makes contact is the SCSI
databus. Say goodbye to most, if not all devices on that SCSI bus.
_____
|_____| ------------------------------------------------- ---+---+-
| | Russell King rmk@arm.linux.org.uk --- ---
| | | | http://www.arm.linux.org.uk/personal/aboutme.html / / |
| +-+-+ --- -+-
/ | THE developer of ARM Linux |+| /|\
/ | | | --- |
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