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    SubjectRe: Core dumps & restarting
       From: Systemkennung Linux <>
    Date: Tue, 29 Oct 1996 04:59:00 +0100 (MET)

    The big problem with freezing processes or machine state and restoring
    it later is that the context gets partially lost like non-local network
    connections. Some code dies because time suddently warps. Or where
    to position file pointers when restoring a process? This is usually
    trivial when the file hasn't changed since taking the snapshot but
    can get very hairy otherwise.

    This depends upon how short you can get "later" and how much state you
    can fully save. Behold...

    We can already do things (generic unix'y speaking) like dump a
    complete core image of ram onto a disk when we punt, and we have the
    technology for multiple initiator SCSI configuarations and to make
    that work.

    Why not dump the core ram image to another "machine", drop
    reservations on all the SCSI devices you are talking to, and then tell
    the machine "mount my disks, assume my ip addresses, and act like me,
    because I'm going down". It can work with something like a 3 minute
    max takeover time if you do it right. If the panic'ing machine can
    come back up cleanly, the transfer of core image can happen again,
    scsi device ownership given back, ip interfaces set back up, and you
    are _still_ back in operation. You can get it so good that it only
    looks like the network is saturated to your users ;-)

    This idea only is useful when you hit the point that you can get the
    machines running, image cloned and operational, somewhere else within
    the timeouts for various things like tcp connections etc. And now you
    are getting to the point where the delay is about the same as you'd
    see if the machine was swapping a lot or otherwise heavily loaded.

    Yes, I've been thinking about stuff like this.

    David S. Miller

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