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Re: [Xen-users] Does XEN support crash carts?

To: "Mark Williamson" <mark.williamson@xxxxxxxxxxxx>, "Steffen Hulegaard" <shulegaa@xxxxxxxxx>
Subject: Re: [Xen-users] Does XEN support crash carts?
From: "Nico Kadel-Garcia" <nkadel@xxxxxxxxx>
Date: Fri, 9 Mar 2007 00:14:33 -0000
Cc: "Foreman, Tim" <tforeman@xxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx, Jayson Vantuyl <jvantuyl@xxxxxxxxxxxxxx>
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Mark Williamson wrote:
     Awesome answers!  The XEN community rocks!

     It now seems as if there is shred of truth
to the 'myth'.  Still, XEN already has almost
everything anyone might want - so I'm thinking of
ways I might contribute to fix what I'm thinking
might be a *very* smallish XEN limitation.  Please
bear with me.  I'll attempt to explain.

OK, cool.

     Recall from the beginning of this
thread that I mentioned that VNC is almost
always good enough.  I was bringing up the
very rare 'crash cart' case.  For instance,
a NIC card might be down/dysfunctional.
Even with a down NIC, the null modem (cross-over)
cable to the physical serial port works
(as explained - Dom0 mediates/relays the chosen
DomU serial traffic, etc.).  However ... unless
I misunderstand something about VNC, VNC is
*NOT* going to work with a down NIC.  If I
recall correctly, VNC requires a TCP/IP
connection.  Of course, I'm newbie ignorant
of any special features tha might have been
added to XvncD.  Am I spouting nonsense here?

No, you're not.  However, if you install a VNC viewer on dom0 then
you could fire it up on dom0's local console and get access to the
domU framebuffer that way.

You could also set up PPP to provide and route an alternate network path over a serial port. Me, I keep a spare USB/100baseT adapter around for just such moments to avoid being too off-line to get the drivers for a network card, or to help backup a machine due for hardware maintenance and unable to use the NIC for whatever reason.


     So, in the glorious ignorance of a newbie,
I'm guessing that the physical VGA/USB ports
are not 'active' (on the back of the box).
Any attempt to cable up a crash cart LCD/monitor,
keyboard and/or mouse, to these inactive
physical ports, will not work.  Right?  Or
did I miss something major?

They'll work, you just can only get domain 0 talking to you.  So
you'll have dom0's VGA and USB connections; fire up the VNC viewer in
dom0 and you'll be set.

With what I described, the USB port can provide a normal network access without using the NIC. You'll have to reconfigure the DomU's to use it, but it's workable.

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