Re: RAID 1

From: Les Mikesell (lesmikesell_at_comcast.net)
Date: 12/28/03

  • Next message: Leon.: "Re: Handling a large number of IPs efficiently" 
    Date: Sun, 28 Dec 2003 07:15:41 GMT

    "P.T. Breuer" <ptb@oboe.it.uc3m.es> wrote in message
    news:qj6lsb.fvt.ln@news.it.uc3m.es...

    > > The question was obvious from the first post: "when you have mirrored
    >
    > What "first post"? This is usenet!

    Yes, usenet messages are threaded and reasonable readers can
    traverse the list backwards to the beginning of the thread.

    > > partitions, how do you convince grub to make both drive's boot sectors
    > > bootable so that you can continue using the machine after the primary
    >
    > Are you sure you mean drives and not partitions? It is most unusual to
    > mirror whole drives because raid devices are not partitionable
    > themselves, and because the kernel relies on the *partition* typelabel
    > at boot to know if it is a raid device or not.

    That is precisely the problem. You create mirrored partitions. Update
    your kernel a few times, then the primary drive breaks. You have
    still have a copy of everything, but because grub didn't make the
    drive containing the still-working mirror partition bootable, you
    can't use it.

    > Perhaps you are running lvm over the raid1 device, in order to provide
    > partitions?

    Well, that might be a problem if Redhat's installer would actually
    install on lvm but I've never seen it work. It will install on
    mirrors but leaves the mirror unbootable.

    > I don't understand your question - why should you care if grub puts it
    > there or not? YOU can put it there, using the "cp" command, if grub
    > puts it anywhere at all. You will have more problem with getting grub to
    > locate the second stage loaders physical location on disk!
    >
    > So, give us a clue, what *is* your problem, exactly?

    As you've pointed out, it isn't simple to describe to grub how to
    make the drive containing the spare partitions bootable, and after
    going to the trouble and expense of mirroring the data it would be
    nice to be able to use it when the primary drive fails. So, that is
    the problem. Lilo seems to know enough about md devices to
    make both mirrors boot. Grub doesn't, but it has some other
    advantages and is now the default in a RedHat install. What does
    it take to make grub know as much as lilo about md partitions? Or,
    if grub can't do it, what command would you issue to make sure
    the non-primary mirror will boot. 

    ---
   Les Mikesell
     lesmikesell@comcast.net
  • Next message: Leon.: "Re: Handling a large number of IPs efficiently"

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