 Homebrew High Availability: Booting Linux from a RAID-1 Device
Drew Smith
Recently, a colleague told me about a trick his company uses to make Windows NT remote administration easier. His firm provides professional services for many small server rooms around town, and the trick involved mirrored IDE hard disks in removable drive bays — by mirroring the primary disk, you provide an easier backout path when doing upgrades. When doing service work, he always removes the second hard disk, providing an up-to-the-minute backup in case, for example, the latest Microsoft "Service Pack" does more harm than good.
My first reaction was to say "Of course, you can do that in Linux!". However, it brought to mind a few questions — most importantly, just how would you go about doing this? I mulled it over and eventually decided to explore it on my own. I found that it was possible to boot Linux from a software RAID-1 device, along with a few LILO and mkinitrd tricks, and this little hack could potentially give your Linux Web server a performance boost. In addition to doubling the reliability of your hard disk, RAID-1 configuration also gives your IDE or SCSI bus a break, providing two different paths from which to read the disk. Of course, write operations will be slower because the data must be written to the drive twice, but in many situations (most commonly Web servers, where read operations are a top priority), slower writes are not a drawback.
This is a project for anyone with a Linux machine. If you're new to Linux, you'll need a solid understanding of hard-disk partitioning and the Linux command line, but it's surprisingly easy and fun to do.
Getting Started
The machine you choose to work with probably shouldn't be a production server. As with any project that involves partitioning, you will run the risk of losing data.
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