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From: dav@genisco.uucp (David L. Markowitz)
Newsgroups: comp.unix.wizards
Subject: Panic button SCSI disk reformat!
Message-ID: <1989Oct27.222806.28576@genisco.uucp>
Date: 27 Oct 89 22:28:06 GMT
Organization: Genisco Technology Corp.
Lines: 47

I have a strange problem:  for reasons too horrible to repeat here,
I have been requested to implement a panic button on a Sun system
which, when pushed, will caused the (embedded SCSI) disk to be
reformatted completely (note: not overwritten, it MUST be reformatted).
It would be nice to erase RAM, too, but let's not get greedy.

I have a wide variety of choices on how to implement such a beast.
The ones I have considered include:

	1. The button triggers a bit on a VME board which is either
	   periodically polled, or causes an interrupt, to a daemon
	   which then reformats the disk.  (I already have this
	   board - that part is easy).  This will be harder on
	   non-VME Suns, but that's another problem.

	   a. This daemon must be static and locked in RAM, to avoid
	      it dieing when its swap or image are erased.  I don't
	      know to keep the OS from dying, though.  Or,

	   b. The daemon does an ioctl() to the board's driver,
	      which (as a piece of kernel) raises spl all the way
	      up and shoves the format commands down to the disk.
	      (I don't think the SCSI command set includes one
	      to "format the whole thing and ignore me until done",
	      does it?)

	2. The button triggers a piece of hardware attached to the
	   SCSI bus which sends the appropriate SCSI commands
	   down the bus.  I guess it should never "Disconnect",
	   or something like that (I'm no SCSI expert).


Solutions based on #1 (primarily software) are cheaper, but less
reliable (OS down, CPU overheated, fragged, etc).

Solutions based on #2 (hardware) are more expensive, take more room
and power, and generate more heat.  Of course this box could fail, too.

Have I missed any solutions?  Does anyone have something like this
in place?  Please mail ideas.  I will summarize if there is any
interest.

	David L. Markowitz
	Genisco Technology Corporation
	dav@genisco

-- 
	David L. Markowitz
	Genisco Technology Corporation
	dav@genisco