[3902] in linux-scsi channel archive
Re: questions about external SCSI -Reply
daemon@ATHENA.MIT.EDU (Harvey Fishman)
Tue May 12 11:47:55 1998
Date: Tue, 12 May 1998 11:32:23 -0400 (EDT)
From: Harvey Fishman <fishman@panix.com>
To: Jeffrey Waters <Jeffrey.Waters@rich.frb.org>
cc: ulisses@pusa.eleinf.uv.es, linux-admin@vger.rutgers.edu,
linux-scsi@vger.rutgers.edu
In-Reply-To: <s5582abc.034@richmail>
On Tue, 12 May 1998, Jeffrey Waters wrote:
> I would not recommend doing any equipment connections unless you are
> using Hot-Plug hardware, you will risk damage to both the device and the
> controller.
Oh come on. Not with SCSI; the only signal line that has ANY oomph to it
is TERMPWR and in a properly configured bus that is fused at 1 Ampere or
current limited at a similar value. SASI was a different story as there
the TERMPWR line was NOT limited and there are many urban legends of this
causing fires.
What you risk is damage to data, as the sudden change in the environment is
likely to do nasty things to any traffic on the bus at the time of the
change. But if you can find a time when the bus is idle, then there should
not be any problem at all. Getting the system to recognize the new device
is another story entirely. But as my Apple friends tell me that this is
directly supported by both Apple hardware and software, it should be quite
possible.
The main thing that hot-plug does is use connectors that assure that earth
contact is made before any signal lines are connected to minimize trauma
and to use solid device mounting rails to be sure that those connectors can
work properly. Other than that, there is software to maintain the system
registration by continuous device polling. In a typical normal system that
is only done once at boot.
Harvey
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Harvey Fishman |
fishman@panix.com | A little heresy is good for the soul.
718-258-7276 |
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