Mirror, Mirror on the Drive

Let’s face it: small businesses don’t back up their hard drives often enough, and they can’t afford fancy RAID hard drives to protect against data loss.

But hard drives and fans, being the only mission-critical moving parts in servers, are among the most likely to fail.

Adding a mirrored hard drive is a cheap and easy way to protect your Windows 2000 server from data loss, and this article will explain how to do it. (Sadly, Windows 2000 Pro and Windows XP do not support software mirroring.)

First, a quick explanation of how it works: Windows automatically keeps both hard drives in sync without bothering the end user. Every time a file is saved, it’s saved on both drives. In theory, if one drive starts experiencing errors, Windows gracefully handles it and uses the good drive instead. In practice, when one drive fails, the server runs sluggishly, hesitating while it waits for the bad drive to get its act together. While this can be disturbing from a user’s perspective, the good thing is that no data is lost as the drive fails.

Start by purchasing and installing a second hard drive. The second drive needs to be at least the same size as the original drive that’s being mirrored, but it doesn’t have to be exactly the same size.
Start the computer and go into the Control Panel, Administrative Tools, Computer Management. Click on “Disk Management” and a window will come up showing the drives and partitions. Right-click on Disk 0 (not the C: partition, but the Disk 0 label) and a dropdown menu will pop up that offers to Convert to Dynamic Disk. Check both Disk 0 and Disk 1, and we’ll kill two birds with one stone.
VolumeManager users may get an error message saying “Logical Disk Manager cannot proceed with the conversion. At least one disk does not have enough free space to perform this conversion.” Dynamic disks require 1mb of free space on the drive. While Windows automatically reserves this space when doing formatting, programs like VolumeManager and PartitionMagic do not. Users of these wonderful programs will need to dig them back out again, resize their partitions to create a few megs of space at the end of the drive, and then try this process again.

Windows will warn that the drives will be dismounted, which means that all files on the drives will be closed, and then it reboots to complete the conversion. Being Windows, after it reboots, it may say that it needs to reboot yet again. Let it. Be one with the reboot. (Or perhaps, be two with the reboot.)

After the reboot, go back into Control Panel, Administrative Tools, Computer Management. Click on “Disk Management” and now both disk drives show up as Dynamic Disks. Right-click on the C: drive and click Add Mirror. Choose Disk 1 as the disk to use as the mirror, and click Add Mirror. Windows then starts copying the contents of the first hard drive’s C: partition over to the second hard drive. It’s transparent to the end user, but it shows in the Disk Management screen. It’s like watching grass grow, and less exciting, but at least network users are not affected during the process.

If the server has more than just a C: partition, like a D: and E: partition, right-click on those and click Add Mirror as well. Windows manages the partition copying process: technically, there’s no need to wait for the C drive mirror to be complete before adding the D mirror, but I like to wait just to know that the C mirror is absolutely done to make sure it worked, and to keep the speed from affecting the end users.

When it’s all said and done, the Disk Management screen will look something like the screen shot shown. Notice that the bar graph sizes for the two C: partitions aren’t identical: that’s because the two drives are not identically the same size. The second drive that was purchased for mirroring purposes was about 1.3 gigabytes larger than the first drive. That second, larger drive therefore has a bar at the bottom right that says “1.34 GB Unallocated”, and since both bar graphs have to have the same total size, Windows resizes the bar graphs to make it nice and even. That’s misleading, because it suggests that the two C: partitions aren’t the same size. Look closely, and Windows shows both at 9.74 GB.

Eagle-eyed readers will notice that the E drive on this particular server is labeled “mp3”. Years ago, I spent several days ripping my collection of over 400 music CDs to MP3s. Should that hard drive fail, it would take me another several days to rip those CDs again – and sooner or later, that drive will fail. The cost of an $80 mirrored hard drive is worth not having to hassle with shuffling 400 CDs in and out of my CD drive. If it’s worth $100 to me to protect my music collection, isn’t it worth the $100 for your small business?