Like the eponymous bug spray, RAID gets results. But in this case, the active ingredient isn’t a deadly poison, but hard drives—or, to spell out the acronym, a redundant array of independent (or inexpensive) disks.

RAID represents a storage schematic, a way to use multiple hard drives to accomplish wondrous achievements in automation and capacity. You can chain a number of drives together to create one large super-volume, you can have one drive automatically replicate the contents of another, you can do it all!

So where do you start? With this guide, because while RAID may sound simple, the actual practice of setting up an array is mildly daunting. But before we start attacking the various configuration options that smack you in the face with every RAID setup, we’ll start with the easiest part first, the shopping list.

To set up a RAID, you’ll need at least two items: a motherboard with the ability to create and manage RAID volumes and some hard drives. The exact number of drives will depend on the flavor of RAID you choose, the level of performance you hope to achieve, and your budget, but the drives should be of an identical make and capacity, as your RAID configuration will always be limited by the speed and size of the slowest drive. If you’re planning to string together more than four drives, you’ll likely need to invest in a RAID controller card as well (check your motherboard manual for details about its integrated RAID support).

RAID 0

The RAID variant that offers the fastest speeds and most capacity also comes with the biggest worries

A RAID 0 setup is commonly known as a striped array. Instead of writing all of your data to a single drive, this configuration allows a file to be broken up into smaller chunks, or stripes, which are then written across all the drives in the array. The more drives you add to a RAID 0 config, the faster the overall performance of the array. After all, by adding drives, you’re just spreading out the workload.

To really get the most from RAID 0, you’ll want to play with the stripe sizes. We say play, as there’s no concrete way to gauge what stripe size will be best for your particular setup—short of testing its performance with the apps you’ll be using.
If a file is a pizza, then a stripe is a slice. Slap a 50KB file onto a four-drive array with a 16KB stripe size, and three hard drives will have full 16KB stripes while the fourth will have just 2KB. The sizes affect RAID performance because using smaller stripe sizes often spreads the simultaneous writes and reads across multiple drives, which improves transfer performance for larger files. Using larger stripe sizes allows a single file to be split across fewer disks and, if your RAID controller allows it, will free the unused disks for other access operations. This improves the ability of the drive heads themselves to get to the part of the drive platter with the data.

Hands On

We used four Western Digital Raptor drives in our RAID 0 testing, with a fifth Raptor for the Windows partition. We experimented with stripe sizes ranging from 4KB to 1,024KB, measuring performance with the HD Tach and PCMark05 benchmarks. We achieved the best results with a 128KB stripe size. Using this size, we compared the performance of both a two-drive and four-drive RAID 0 config to that of a single Raptor.

As you’d imagine, the four-drive RAID 0 setup produced the fastest speeds in our benchmark tests. But even striping two drives together gave us a pretty awesome advantage over a single drive. The PCMark05 scores weren’t as much of a blowout as the HD Tach benchmarks, but they nevertheless show that our RAID array is faster than a single drive in every single benchmark the program has to offer.

This immense power, however, comes at a great cost—namely, the safety of the data stored on the array. For if a single drive in your setup fails, that’s it. Your data’s gone. On a two-disk array, striping doubles your chance of data loss due to drive failure. And that risk only increases as you add more drives to the mix.

Two Terabytes? Denied!

Wait! Before you start building a super-array of drives, know that Windows XP does not support partitions greater than two terabytes. It’s just not happening. If you want to, say, chain four terabyte drives together, you’re going to need Windows Vista and a fifth hard drive, because even Vista can’t boot into the partition scheme you’ll need to set up, unless you have an EFI motherboard.

GPT, or the GUID Partition Table, is an updated version of the Master Boot Record partitioning scheme that will let you break through Windows’s 2TB limit on disk sizes. Install the OS on your separate hard drive, then set up your RAID 0 config. When you initialize the disk in Vista’s Computer Management window, make sure you select the GPT partition style instead of MBR.

RAID 1

Making a spare copy of your data will impact performance, but by how much?

Otherwise known as disk mirroring, RAID 1 maximizes protection between two disk drives. Unlike a RAID 0 setup, two drives linked in a mirror configuration don’t double the total capacity of a single new volume. Rather, the capacity of the volume is determined by the size of the smallest drive in the array.

The benefit of mirroring two drives together is obvious; just consider the name of the array. Whenever data is written to a single hard drive, it is instantaneously written to the other drive in the array as well. If one drive fails, you’ll have a copy of all your data. You can then boot off of the survivor by itself or replace your busted drive in the array with a working drive. Your RAID controller will rebuild the array without interrupting normal file operations and return everything to full working order.

This kind of setup is ideal for those who are more concerned about protecting their data than increasing performance. However, don’t misconstrue the benefits of RAID 1 for a data backup solution. A mirrored array is more designed for those, “Oh crap, the hard drive just died randomly” scenarios. A mirrored array won’t protect you from accidental file deletions or malicious software that wipes out your drive (see the sidebar below).

Hands On

Due to the extreme differences between RAID 1 and RAID 0, we expected to see dramatically different results in the relative speeds of the two formats. After all, you’re trading storage speed for sustainability. What we were unsure about was the performance difference between a mirrored setup and a single identical drive in a stand-alone configuration.

As it turns out, the mirrored array actually performed better than a single Raptor. We attribute this to our RAID controller’s ability to select which drive to read data from—it can use one hard drive for one data task, while simultaneously accessing a different data request with the other. Not surprisingly, the mirrored array’s write speeds weren’t as impressive but still bested a single Raptor drive by about 7MB/s.

RAID 1 As a Backup Solution? No way!

If one drive’s contents are always replicated on another drive in a mirrored RAID configuration, RAID 1 is the perfect backup solution, right? Wrong. Using a mirrored RAID as your de facto backup solution works wonders in certain disastrous occurrences, like if one of your hard drives spontaneously explodes. But RAID 1 doesn’t prevent any of the more malicious (or user-created) data loss issues. If you have a virus on one drive—guess what?—it’s been replicated on the second drive. Or if you accidentally perma-delete a file, it’s gone on both drives. Grab a third-party backup program for your files and let RAID 1 take care of the act of God–type situations.