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    SubjectRe: Does this help explain better?? ATA/IDE Thread
    re: S/390

    if I understand it correctly the S/390 can partition itself on the fly to
    run multiple operating systems (including multiple copies of the same
    OS) so all you would need to do is to start a new copy of linux that has
    the filter turned off and you can get access to your hardware.

    David Lang

    On Wed, 26
    Jul 2000, Malcolm Beattie wrote:

    > Date: Wed, 26 Jul 2000 12:58:30 +0100
    > From: Malcolm Beattie <mbeattie@sable.ox.ac.uk>
    > To: James Sutherland <jas88@cam.ac.uk>
    > Cc: Stephen Frost <sfrost@ns.snowman.net>,
    > Horst von Brand <vonbrand@sleipnir.valparaiso.cl>,
    > linux-kernel@vger.rutgers.edu
    > Subject: Re: Does this help explain better?? ATA/IDE Thread
    >
    > James Sutherland writes:
    > > On Tue, 25 Jul 2000, Malcolm Beattie wrote:
    > > > Me:
    > >
    > > > > Upgrading firmware would typically be an unusual enough event the reboot
    > > > > wouldn't be an issue. In the environments where a reboot is unacceptable,
    > > > > a firmware change on-the-fly would probably be unacceptable too...
    > > >
    > > > On the contrary, on important 24x7 systems you don't want to have to
    > > > arrange for downtime just to update firmware/microcode.
    > >
    > > I didn't say you would. My point was that changing firmware live on a
    > > production system where any downtime is critical would not be very safe.
    >
    > Your point is wrong. You are wrong. Changing firmware on a live
    > production S/390 system is safe, supported and has been done for
    > years if not decades (I don't know when CMLIC was introduced).
    >
    > > > S/390 already supports this (running Linux under VM and maybe running
    > > > it in an LPAR or raw, but I'm not sure) under the name "Concurrent
    > > > Maintenance of LIC" (LIC being Licensed Internal Code, the equivalent
    > > > of microcode or firmware). This includes processors. As other
    > > > architectures begin to play in the five-nines arena, we don't want
    > > > Linux being left behind on those architectures just because of some
    > > > "oh, you can always recompile the kernel or reboot" mentality.
    > >
    > > In the case of hard drives, they should be hot-swappable in this
    > > environment - in which case, you can remove them, upgrade them off-line on
    > > a spare workstation, then restore them once you know they work.
    >
    > Stop thinking only about small systems. Linux runs on large systems
    > too. We are talking about systems with maybe hundreds of disks. Not
    > only would it be time consuming to hot-swap them all one at a time
    > but, in the case of S/390, you're going to have difficulty finding a
    > separate system in which to hot-plug the disks. Your "spare
    > workstation" would have to be a P/390 with real channel hardware
    > attached. This is not the way that things are done.
    >
    > > What would you have done in your production system if the firmware upgrade
    > > had, say, upset the SCSI ID selection so it conflicted with another drive
    > > in the RAID array? You just lost two drives at once. Or, worse still, if
    > > it starts flooding the bus with crap, because the firmware upgrade went
    > > wrong, or the image had a bug in??
    >
    > Stop thinking about small systems. You have RAID across multiple busses
    > (not SCSI) with channel multipathing and hot-boxing. If firmware
    > upgrades caused such problems then IBM and the other PCMs would have
    > had much egg on their faces and fixed it. Trying to physically remove
    > every disk, channel and PU just to do a firmware upgrade on it is far
    > worse. It would be similar to requiring disk removal just to do mke2fs.
    > And why are your expecting firmware upgrades to go wrong? Do you really
    > think a large system vendor would supply untested or broken firmware
    > upgrades for a high-reliability system? Once again, stop thinking about
    > small systems. (Oh, and even if a channel is flooded with crap, the
    > system will automatically hot-box it and choose another path to the
    > necessary devices transparently, assuming you've multipathed them as
    > you should).
    >
    > --Malcolm
    >
    > --
    > Malcolm Beattie <mbeattie@sable.ox.ac.uk>
    > Unix Systems Programmer
    > Oxford University Computing Services
    >
    > -
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