Redundant and fault-resilient hardware is a good idea for any critical server, but this precaution doesn't render you impervious to downtime. Software corruption happens even on the most fault-tolerant hardware, so consider supplementing your NT recovery toolbox with a few other tools, including an alternate/parallel Windows NT installation.
A parallel installation is a secondary NT installation that resides on the same drive or a different drive from the primary installation. A parallel installation acts like a back door to your system by letting you access files on NTFS volumes and system Registry data when your primary installation is down. This accessibility means that you don't rely on NT Setup's Repair process to recover your system.
You can choose the destination directory for a parallel installation, but I recommend a directory that identifies its nature as a recovery boot. For example, I install a parallel installation on every server I set up for my clients and place the installation in a directory called \winntrec (i.e., Windows NT recovery). For maximum protection, place this installation folder on a separate partition or physical drive.
When you install an alternate NT installation, don't duplicate all the primary installation's options (e.g., networking services, NT's server role). Install the minimum options for the parallel installation to conserve disk space. For example, I clear NT's accessory dialog box options during the parallel installation's setup, and I usually don't install networking. However, if you'll require access to other machines on the network while you're booted under the alternate installation, install networking components. In addition, installing the latest service pack isn't a necessity—install a service-pack level that you're comfortable with, but you don't have to keep the alternate installation in lockstep with the primary installation's service-pack level.
Another good practice to add to your recovery toolbox is to install the backup software you use on your network into your parallel NT installation. That way, your alternate installation is ready to quickly restore system data or files from the primary installation.
Finally, parallel installations are most handy when they exist before a problem arises. Although you might be able to install a parallel NT installation after the primary installation goes belly up, this isn't a good time to do so. At the least, scrambling to install a parallel installation significantly increases the amount of time you need to recover the server. At worst, the primary installation's problems might interfere with your ability to successfully complete a parallel installation. I strongly recommend that you consider parallel NT installations a default feature for all your servers—parallel installations will save your sanity if something goes wrong.