Re: [Little OT] grub and udev root device
On Fri, 04 Aug 2006 08:38:28 -0400, Scott Reese wrote
> Greetings:
>
> Our setup here is a little different than yours, but it should work the
> same. We are doing software RAID1 across two SATA drives.
>
> The controllers that we have (low-end HP hardware) control which
> drive appears where in the chain. The drive plugged into connector
> 0 is sda and the drive plugged into connector 1 is sdb. When we
> lose sda, sdb stays sdb.
>
> Additionally, mdadm can tell which drive is which. I'm not sure if its
> writing some identifying information onto the drive or what, but each
> disk seems to know its place in the configuration.
>
> One thing that you are going to want to make sure that you do is to use
> the grub console to place an MBR onto each of the drives in the
> array, not just the first one. Otherwise, if you remove drive sda,
> the machine will look for an MBR from sdb, not find one, and not boot.
>
> Our servers do not have hot-swappable drives, so we have something
> of a problem when we lose sda. We have to shut down the box to
> replace the drive, but then the replacement sda drive is blank, and
> the controller can't boot from it. Some of the machines have BIOSes
> that will let you pick which drive to boot from, others require a
> grub boot floppy or USB stick from which you can direct the machine
> to boot from sdb. Check your BIOS before disaster strikes.
>
> Nothing replaces some good testing. Before you place the box into
> production, play with it. Shut it down, pull sda, and boot it up. See
> what happens. Then you'll know exactly what steps are required in
> the event of a failure, and when it happens with real data on the
> box, you'll know what to do. You might even document the required recovery
> steps, print them out, and attach them to the machine. The next person
> who has to maintain the box will thank you.
Thanks for the info, good stuff.
Thats similar to what we have.
Except we run 4 drives (partitions) in a raid 1 mounted to /boot.
Grub is installed to the MBR on all 4 drives.
Then we run / on a raid 10.
We use mostly gigabyte, intel and asus boards, and from what I can tell, if
a drive dies, the rest do not stay as they should. They just move down the
chain.
Whats interesting is we see that most drives simply fail, or begin to show
symptons of failing. It always shows up, but will never work right.
Therefore we can catch it, replace it before it becomes invisible to the
computer.
But in the rare case that it did become invisible, I was originally worried
that the software raid would become corrupted.
Thanks to Len for clearing things up about how mdadm works, (arrays are
built using UUID instead of devices alone) and this gives me confidence that
we could have a drive die, power loss, reboot and no one would know the
difference.
Cheers,
Mike
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