In-Depth

The Mirror Crack’d

This author figured that mirroring his e-mail drive was solid insurance against data loss. That theory was tested to the max when a drive failed.

I was just getting settled in to answer the overnight e-mail when I discovered a curious thing: The computer where I do 90 percent of my work was locked solid, not responding to the keyboard or the mouse. After a bit of futile pounding on the keyboard, I rebooted and then logged in to a system that seemed to be responding very slowly. A bit of poking around in the Event Viewer and Disk Management tools showed me the reason for the slowdown: The mirror set that includes my boot drive was busy re-synching. Worse, the System event log was showing such cheerful messages as, “dmio: Fail to reassign bad block(s) on disk Harddisk0: error 0xc0000010.”

OK, so this was a nuisance, but not a disaster. I congratulated myself on having the foresight and paranoia to keep my e-mail on a mirrored drive and went out to buy a replacement for the failing disk. A bit later I was home with a new 80GB drive and a simple plan: Break the mirror, add the new drive, rebuild and all would be well. I figured I’d be done in half an hour, tops.

My development machine is set up with its boot drive as e: and no c: drive (you’d be surprised how many software bugs this arrangement catches). So, knowing that drive 0 (zero) was failing, I wanted drive 1 to remain the e: drive after breaking the mirror set. Windows Server 2003 help says, “The volume copy you click to break the mirrored volume retains the drive letter or mount point, while the other volume is assigned the next available drive letter.” So I clicked on drive 1, told it to break the mirror…and was suddenly looking at drive 0 remaining e: while drive 1 became c:. Apparently things don’t work as documented, at least on the boot volume. And, of course, there’s no “undo” in Disk Management.

Not knowing what else to do, I shut down the computer, removed the failing drive, stuck in the new one and turned the power on. The computer happily informed me that there was no disk in drive a: and no boot device on the SCSI chain (I’m using IDE drives in this box). That wasn’t excessively helpful. After repeating the steps with the same result, I tried just booting with the original drive 1 in place and the new drive not attached. That, at least, got me to the Windows login screen.

It sure didn’t want to get me any further than the login screen, though. I could hit Ctrl-Alt-Del and type in my password, and the computer would repaint the screen and play the happy “Welcome to Windows!” sound. Then…it went right back to the login screen. This wasn’t encouraging.

Faced with a previously-unknown symptom, I did what any MCSE would do and searched the Knowledge Base. Somewhat to my amazement, this turned up article 249321, “Unable to Log on if the Boot Partition Drive Letter Has Changed,” which described the problem perfectly. For resolution, it led me to article 223188, “HOW TO: Restore the System/Boot Drive Letter in Windows,” which has a step-by-step procedure for using regedt32 and regedit (yes, you need both) over the network to fix the problem.

Fortunately, I’ve got a lot of other boxes on my test network, so I was able to get in to the Registry and change the drive letter back to e:. With that change, the machine booted, and I was able to log in. Of course, the problem remained: Now I had a non-mirrored drive and a new drive sitting on the desk. Why wouldn’t they both coexist happily?

It was about three reboots later that I finally did what should have been obvious and checked the jumpers on the drives in question. Though the new drive was set up for “cable select” (like just about any other drive sold in recent memory), it turns out that the old one was actually jumpered to “slave.” This proved to be an unworkable combination for identifying a boot drive. I moved the old one to cable select as well, made sure it was on the master position of the cable, and the box booted just fine. Then, it was just a matter of waiting half an hour for the mirror set to rebuild…two hours later than my original optimistic estimate.

About the Author

Mike Gunderloy, MCSE, MCSD, MCDBA, is a former MCP columnist and the author of numerous development books.

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Reader Comments:

Fri, Mar 19, 2004 Donald Xie Australia

I enjoy this article - we've all seen or done something of the same category. I also think the critics are wrong - we all make mistakes and it's more important to learn from the mistakes. Now I'm pretty sure that many who have read this article will have this in mind in our next trouble-shooting session.

Thu, Feb 12, 2004 Anonymous Anonymous

Or maybe MCP Mag. should vet cruel critiques that might discourage future contributions that could help some readers.

Sat, Feb 7, 2004 ApprenticeGM Central Coast, Australia

As an MCSE myself I'm stunned you wouldn't check the jumpers on an IDE device first. I think also that MCPmag should start to vet contributions like this - it'll encourage no end of users to think this is acceptable. You make a mockery of the MCSE cert.

Fri, Feb 6, 2004 Edi US

Thanks for sharing, it reminds us all to not forget the "obvious" which are always obvious in retrospect.

Fri, Feb 6, 2004 Anonymous Anonymous

and then we wonder why our hard earned certs are worth nothing .... have you seen the mcse req for "field experience" ?? where did you train for your exeams , braindump ???? start with an a you'll be at your place , anyway software raid on IDE drives ....... besides your home lan in your basement what do you support ?

Fri, Feb 6, 2004 Anonymous Anonymous

and then we wonder why our hard earned certs are worth nothing .... have you seen the mcse req for "field experience" ?? where did you train for your exeams , braindump ???? start with an a you'll be at your place , anyway software raid on IDE drives ....... besides your home lan in your basement what do you support ?

Thu, Feb 5, 2004 Anonymous Anonymous

Excellent example for a "paper" MCSE

Wed, Feb 4, 2004 Higgins NJ

I learned early on to never use software mirroring. These days you can get an IDE RAID controller for $70. With hardware, the OS just sees another volume, plus you eliminate the overhead of the OS handling the RAID.

If you'd had a RAID controller you could have just shut down, replaced the drive, and rebuilt the mirror set on the way up.

Wed, Feb 4, 2004 Anonymous Anonymous

wonderful real life scenario

Wed, Feb 4, 2004 Anonymous Anonymous

Good article that presents MS with the problem of Hardware dependency. Why would it lock for Master or Slave??? In any case go with hardware raid on the server, I say, few more $$$ less headache.

Mon, Feb 2, 2004 stvrjk Redwood City

Reading the first sentence said ... sloppy. While it's fine as a reminder that mirrors can always present more problems than not, it wasn't worth the read. Cable select and not checking jumpers ... speechless.

Sun, Feb 1, 2004 Webtek Concord

I've had experiences in the past that have forced me to use a Microsoft Engineer to resolve a problem. Their recommendation, as well as the recommendation of other TEchies, is to set all drives to Master or Slave appropriately. Using Cable Select is not recommended in a Microsoft Enterprise OS.

Sat, Jan 31, 2004 Anonymous Anonymous

all that for email. better off backing it up on a different machine 3 MC's need 1 DJ.

Sat, Jan 31, 2004 MCSEx2 Anonymous

Good Story!

Fri, Jan 30, 2004 Anonymous Anonymous

Very good - sometimes it's easy to overlook to obvious.

Fri, Jan 30, 2004 Anonymous Anonymous

All those MCs and you didn't check the drive jumpers????

Thu, Jan 29, 2004 Tcat Anonymous

Keeps us with jobs, huh?

Thu, Jan 29, 2004 Anonymous Anonymous

There is nothing more dangerous than a developer with a screwdriver. Surprised you found it before rewriting the disk drive API!!

Thu, Jan 29, 2004 David Moss York Pa

Good scenario

Thu, Jan 29, 2004 Anonymous Anonymous

Maybe you should study for your Aplus exam before messing with hardware!

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