Re: Booting Directly from Mirror after losing Primary

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From: Top Hat (Top__Hat_at_RemoveMe.hotmail.com)
Date: 02/16/05 

Date: Wed, 16 Feb 2005 17:00:05 -0500
To: "Mark C. Walton" <MarkCWalton@discussions.microsoft.com>

Mark C. Walton wrote:
> Anyone, feel free to jump in here....
>
> "Mark C. Walton" wrote:
>
>
>>Hi Gerry -
>>
>>Yes, well, I'm moving away from the Windows mirroring as time & resources
>>allow, but for now I'm stuck with it on most of my servers.
>>
>>The complaint I've always had with hardware RAID, as I alluded to, is that I
>>can't mirror on separate controllers, so if a controller goes down, you've
>>had it. I also recently had a hardware RAID controller go bad and spew some
>>garbage onto my disks, making BOTH the primary and the mirror unreadable
>>simultaneously (so obviously the mirroring was still working flawlessly!).
>>Luckily my backup was good, but even so, it was scary.
>>
>>I thought I read somewhere that Windows 2003 DOES mirror "everything" and
>>this isn't a problem anymore, is that not the case?
>>
>>Anyway, I don't think the problem is that the disk isn't active (a la
>>FDISK), because the server will try to boot from the disk (as defined in the
>>BIOS) but I immediately get a disk read error - obviously because Windows
>>doesn't "understand" the disk because it was originally installed onto the
>>old controller & disk. Also, the partition table seems fine because it all
>>looked normal in Disk Management - I was able to easily break the mirror and
>>re-establish it onto the replacement disk.
>>
>>I've thought of running Repair from Setup - then I could hit F6 to load the
>>driver when it starts - but is the repair procedure "smart" enough to then
>>install the driver onto the disk?
>>
>>I guess the basic question becomes, where does Windows look to for the SCSI
>>driver when it starts from the hard disk? I poked around on some of my other
>>servers and can't figure it out. It seems you are in a Catch-22, because it
>>can't read the disk without the driver, yet it can't load the driver without
>>reading the disk. That means to me that somehow when Windows is first
>>installed, somehow it stores the necessary code somewhere that it can read it
>>first in DOS mode or something. Does that make sense?
>>
>>Thanks for your help,
>>
>>- Mark
>>
>>"Gerry Hickman" wrote:
>>
>>
>>>Mark C. Walton wrote:
>>>
>>>
>>>>It was a software mirror...AFAIK, there is no way to do a hardware mirror on
>>>>separate controllers...
>>>
>>>OK, I just wanted clarification.
>>>
>>>Basically software mirrors (as prescribed by Microsoft) are not really
>>>mirrors at all, in that the Intel boot code is missing on the shadow.
>>>
>>>That's my understanding anyway.
>>>
>>>If it was an old broken computer I didn't care about, I'd be tempted to
>>>try marking it as Active in FDISK or hacking it with a sector editor,
>>>but I wouldn't do this on a computer I cared about.
>>>
>>>It's been a long time since I read up on this, but I remember at the
>>>time deciding I'd _never_ use the Windows built-in "RAID" options.
>>>
>>>This is not to be confused with "Dynamic" volumes, which work great on
>>>Data partitions.
>>>
>>>--
>>>Gerry Hickman (London UK)
>>>

Do you have a utility partition of any sort on the original drive? The
reason being is that when you create the dynamic mirror through disk
management, you only mirror the volumes that Windows uses. If you have a
utility partition at the front of the drive (like most HP, Dell, and
otther OEMs do), the offset to teh actual mirror is not correct. This
can be fixed with something like diskprobe if you're feeling up to the task.

If you didn't have the utility partition on the original drive,
something else may be going on.

Try updating your boot.ini to correct the rdisk entry to point to the
second disc.

As for installation, if by "DOS mode" you mean textmode, then yes, the
OS stores a copy of the driver loaded in textmode and it gets copied to
the correct location during GUI mode install.

Does this help? 

---
TopHat

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