What's RAID 10 And Why Should I Use It?

RAID is, of course, a Redundant Array of Independent (or Inexpensive) Disks. It is a method of storing information on multiple hard disks for greater protection and in some cases performance. Under the RAID umbrella are a number of different storage methods, called levels and numbered from 0 to 9, some of which are more useful than others.

Each level is a distinct method of organizing storage, but some of them can be combined which produces a two-digit RAID level, such as RAID 10, sometimes identified (and more appropriately so) as RAID 1+0. In general, each RAID level has its own advantages and disadvantages.

RAID 10, for example, is fast, it's crashproof and it eats disk space. If you need more protection for your storage, or faster storage performance, RAID 10 is a simple, relatively cheap fix.

To implement RAID 10 you need at least two physical hard drives; just using two partitions on the same hard drive is inadequate. You also need a disk controller that understands RAID.

RAID 10 works by striping and mirroring your data across at least two disks. Mirroring, or RAID 1, means writing your data to two or more disks at the same time. Even if one disk fails completely, the mirror preserves the information. Striping, or RAID 0, means breaking your data up into chunks and writing the chunks to different disks in succession. It improves performance because the computer can get data off more than one disk simultaneously. (For the purists out there: RAID 0 technically isn't a RAID level at all because it doesn't provide any redundancy to protect information. However, it is commonly referred to as a RAID level anyway.)

Before we go on, here's one important caveat about backup and RAID 1. Although data is written to two disks simultaneously, the data is not being backed up. Should your system, rather than the hard disk, suffer an error erroneous data could be sent to both disks at the same time, corrupting both drives simultaneously. You still must have a backup strategy in place, even if you use RAID 1. (For greater protection against data corruption, use a RAID level that includes a parity drive, but that's a different story.)

Put RAID 1 and RAID 0 together and you get RAID 10. RAID 10 is secure because mirroring duplicates all your data. It's fast because the data is striped across two or more disks, meaning chunks of data can be read and written to different disks simultaneously.

The drawback to RAID 10 is that it cuts your effective disk space in half. Since everything is mirrored (duplicated), two 60 GB disks give you a total system capacity of 60 GB. And remember, always use identical disks when creating a mirrored array. The disk geometry (number of heads, cylinders, etc.) is critical, and using disks that are different is discouraged in the strongest terms.

Given the cost of disks, storage space is much less of a problem than it was a few years ago. It's cheap enough to add additional disks to support your RAID 10 array and if the disk controller on your motherboard doesn't support RAID 10, you can get an add-in disk controller card for less than $50.

RAID 10 is also slightly more complex to set up than conventional storage, but it isn't particularly hard. The system or disk controller software includes install routines that will walk you through the process. It usually takes just a few minutes to install a RAID 10 array.