I originally started writing this as a how-to on installing RAID on a desktop PC. I came to realize that's not the point I was trying to get across. RAID - specifically RAID 1 (mirroring) - is really just one means to an end. What I really wanted to say was, "Back up that hard drive before it dies!" In the past, I almost religiously backed up my hard disks to tape, but that stopped making sense when my 50GB tapes (compressed) weren't big enough to do a full backup without swapping tapes. That and it took over four hours to complete. With 1TB hard drives now costing the same as a couple of those tapes, there's no reason that anyone should be caught without a complete backup of their desktop. What I see as the current state of hard disk reliability, backups are needed now more than ever.
Sadly, the necessity of having some backup scheme - preferably immediate and constant - has increased dramatically in the last several years. Originally, I would set up a RAID 0 array fully expecting to never replace either disk. The rare occasion when I did have to replace one justified the cost in my mind. I could be quite smug when I slapped in the new replacement disk, chose to rebuild the array, and lost nothing (save the time to rebuild and the cost of the new disk). That fact was that in the early days, the majority of RAID 0 arrays that I set up would go through their entire life with no failures. I know of a couple systems I built running a RAID 0 array that are 4-5 years old and are still on the original drives.
Unfortunately, that's changed. Now, I set up a RAID 0 array fully expecting it to be needed. I'm not sure what's up with hard disk manufacturer's, but reliability just isn't what it used to be. I suppose it could be me; I'm using twice as many hard drives in the systems I build, so it follows I would see twice as many failures. I maintain, however, that's not entirely it. As I mentioned above, my early RAID 0 arrays for the most part ran their entire life without any replacements. In the last few years, more than half of the RAID 0 arrays I've set up have required at least one disk replacement. On my gaming desktop, one of the disks has been replaced twice.
This trend doesn't seem to be limited to a particular manufacturer either. I typically use Seagate or Western Digital (WD), but I have occasionally used Samsung and IBM (now Hitachi) drives as well. I don't use the latter two often enough to include those two in the following statement: In my opinion, no hard drives can be trusted. It seems to be Seagate's opinion, too, as they recently reduced their warranty from five years to three on most drives. (WD was always three years on most drives with a few "enterprise" models at five.) What that should mean to anyone with a drive older than three years is that it should be expected to fail at any time.
I should mention that I used to be a Seagate fanboi; it's the only brand of drive I would use in builds. When I first started using RAID 0 arrays, WD had had a couple embarrassing manufacturing issues to which they responded by initially denying and eventually acknowledging. I wouldn't touch the things. About six years ago, I built myself a new desktop PC with a RAID 0 array using Seagate 120GB drives. One of the drives failed in less than two months. With as many of their drives as I'd used over the years with no failures, I chalked it up to fate and replaced the drive. That is, until the other drive failed within a year. Both were covered by the (then five year) warranty, but that's not the point. Had I not used RAID 0, data would have been lost. I didn't feel I could trust that particular model and moved up to a larger 250GB Seagate. One of those failed two years later. Again, it was still in warranty, but not what I expected from Seagate. RAID 0 was saving the day again and again, but I really wished it wouldn't have had to. I had a similar experience in a desktop PC I built for my daughter. One of the 250 GB Seagate drive failed after about two years. During this same time, the company I worked for bought three WD250 GB external drives for a few of us working offsite. All three died; mine lasted the longest - almost two years. In my opinion, all current hard drives should be regarded with the belief that they will fail before they are out of warranty, so having a backup is absolutely required.
Hopefully, I made a convincing case above that hard drive backup is absolutely essential. It was always a good idea, but with what I'm seeing as the current state of hard drive reliability, it's no longer an option. There are lots of effective ways of maintaining a backup. We'll go into a number of them here and how they affect a new desktop build.
RAID 1 RAID 1, for those who don't know, uses a pair of disks whereby anything written to one disk is also written (i.e., mirrored) to the other. I have been using RAID 1 in desktop builds - both for gaming and business use - for about 7-8 years now. On RAID 1's minus side, half the disk space is lost since two 500GB drives appear as only one 500GB drive. Also, the writes to the two drives require synchronization to ensure that everything was faithfully copied. This slows the write speed of a RAID 1 array down to being somewhat slower than a traditional single disk when not in a RAID.
On the plus side, is that in the event either one of the two disks fails, no data is lost. That's the big plus. Also, when reading files from disk, the RAID 1 array can read alternate blocks of a file from both drives simultaneously to nearly double the read speed. (This is similar to how RAID 0 striping works all the time. See below.) In a gaming system, significantly more time is spent reading from the disks than writing, so even though I am a heavy gamer, RAID 0 gave me a noticeable increase in speed when booting, loading games initially, switching maps/level, etc. When and if a disk fails, that boost in read performance (and the security on having a constant backup) is lost of course.
From a build point of view, the first thing we need is a motherboard that supports RAID or we need to buy a RAID controller add-in card. Most higher-end motherboards support some form of RAID .. usually at least RAID 0 and 1. (More on RAID 0 in a bit.) Motherboards that use Intel southbridge chip ending with an 'R' like ICH9R and ICH10R have some form of RAID support. Motherboards that have an Nvidia chipset such as the 750i or 780i usually support at least RAID 0 and 1.
The second thing we need is a matched pair of disks. Technically, the disks don't have to be the same, but it's more efficient that they are. If a 320 GB drive is paired with a 500GB drive, the resulting RAID 1 array will be 320GB with the extra space on the 500GB drive wasted. If the two drives have a significantly different write times, the effective write time is that of the slower drive. This would waste the potential speed of the (presumably more expensive) faster drive.
When installing the disks, it is best to leave airspace between the drives if possible. If the drive cage has a fan that moves air across the drives, that's even better. The power and data cables should be kept out of the way as much as possible. The picture below shows a pair of drives with a fan in front of them that draws cool air in from the front of the case. (The case is an Antec Nine Hundred.)
Rather than giving instructions for setting up a RAID system here, I'll defer to the large number of guides on the Internet.
Although RAID 1 has saved my hide on a number of occasions, it's only part of a good backup scheme. For example, RAID 1 doesn't protect against accidental deletion of (irreplaceable) files. Nor does it protect against viruses. Therefore, it's still a good idea to perform periodic backup of critical files to CD-Rs, DVD-Rs, an external disk, a spare internal disk, or another computer or network file server. It need not be everything like RAID 1 is, but it should be those documents, audio files, pictures, and movies that you yourself have created and would not be able to replace. Several of the following sections talk about these alternatives.