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Re: Adding devices after boot




Technically speaking, if you power down a SCSI peripheral whose manual 
does not explictely say 'hot-swappable' then you run the risk of 
corrupting the system and/or causing some hardware damage. 

This is because the non-hot-swappable SCSI peripherals have undefined 
states on the bus pins while the power supplies are 'dying' and will 
(could) corrupt any other transfer taking place on SCSI bus at that 
time. Even if there is no transfer the death throes of the SCSI drivers 
in the peripheral could collide with other signals on the bus and cause 
the bus master to fail later (it won't fail with the 1st hundred trials).

Additionally it is a BAD iidea to pull a SCSI plug while the system is 
working, especially for class 1 (metal case) external units. The voltage 
differential between the cases of two machines on the same power plug can 
reach 110 Vac if the grounding is not good on one of them...

On Sun, 7 Sep 1997, Jonathan Ben-Avraham wrote:

> On Thu, 4 Sep 1997, Shlomi Fish wrote:
> 
> > At 03:10 PM 9/4/97 +0200, Gaal Yahas wrote:
> > >Hi.
> > >
> > >I have an external SCSI CD-R that I don't want to be turned on when
> > >not in use. How healthy is is to turn it of while the machine is on?
> > >
> > I'm almost positive that turning off the CD recorder will do no harm as
> > long as it is not used, unless you consider the damage made to the device
> > itself because of frequent power switching.
> > 
> > >How healthy is it to physically disconnect SCSI devices without halting
> > >the machine? What about reconnecting? Possible?
> > >
> > Hmmm, don't know much about SCSI, but as long as the CD recorder is
> > connected to an external socket on a PCI card and is not used when it is
> > disconnected, then I don't think it's much a problem either.
> 
> I have an external SCSI Zip drive connected to an AHA2940 that I 
> occasionally disconnect the power supply from, and then reconnect. 
> Nothing bad happens as far as I can tell.
> 
>  - yba
> 
>    EE 77 7F 30 4A 64 2E C5  83 5F E7 49 A6 82 29 BA    ~. .~   TclTek Ltd.
>  =}-------------------------------------------------ooO--U--Ooo-----------{=
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> 
> 
>