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What exactly is RAID?

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by Dean Barker (4/01/2004)

 

Introduction

RAID (Redundant Array of Inexpensive Disks) is one of those elusive terms that we hear frequently but the bulk of us aren't really sure what it is or can do for us.  Recently, following the review of two AOpen Athlon 64 mainboards that supported RAID, it occurred to me that I understood the basics of RAID but had never run one before.  In doing some online searches, I couldn't find any benchmarks to show what if any measurable performance benefits there are.  With that said, let me take an opportunity to quickly cover what RAID is, what it can do for you and give you some hard numbers to see.

RAID came out of efforts to combine several inexpensive drives to equal or exceed the performance of a larger and more expensive disk drive.  There are lots of different types of RAID that involve the storing of error checking and parity data.  In an effort to not put any of us to sleep and keeping things simple, I want to focus on the two big RAID uses that the vast majority of us could benefit from, RAID 0 and RAID 1. 

RAID 1 is basically a fail safe set up for your hard drive.  Two drives are set up in RAID 1 form which provides all data be written twice.  Once to hard drive A and once to hard drive B.  This set up is for redundancy to keep your data effectively backed up at all times.  You may hear the term "mirroring" when referring to RAID 1.  This is a perfect term because you are making two drives that mirror one another.  Imagine for a second that your primary computer's hard drive just up and dies on you.  While this is rare, it is far from uncommon.  All your data is effectively gone.  Your financial information if you do your bills with something like MS Money or Quicken - gone, the e-mail address of all your friends and even that hot chick from two weeks ago - gone, your term paper - gone, activation codes for downloaded software - gone, etc.  With your drives being mirrored, if one drive dies you still have all your data and remain up and running.  The only downside is that you are halving your disk drive dollar to pay for this redundancy.  Two 80 gb hard drives in RAID 1 give you 80 gb of storage, not 160 if you just had them plugged in as drive C and drive E.  But let me pose a question for you to consider, if your lone hard drive crashed, would it be worth say $75 to have everything back running fine?  I think that says it all right there.

RAID 0 is the performance side of the house.  RAID 0 or "striping" uses two drives in conjunction with one other for speed.  Data is divided when it is written to both drives so that the workload is balanced and thus more efficient.  The data is broken up into chunks or stripes when it is alternatingly stored.  There is no redundancy of data with RAID 0.  You should be using two identical drives if you are setting up a RAID 0 but this is not required.  Two different drives can be used but at a small cost.  Keeping in mind that the workload is being balanced, the computer sets the drives up to be equal.  If you have an 80 and a 120 gb drive, RAID 0 will have your machine treat them as two 80 gb drives, ignoring the extra 40 gb of space on drive two.

The benefits of RAID 1 are obvious but those of RAID 0 are understandable but not exactly clear.  If you are like me you are asking yourself about now, how much of a performance boost do I get by striping my drives?  If an effort to answer this in the most practical of ways, we took a machine we just finished testing with built on an AOpen AK86-L board and altered it by adding in an identical hard drive, formatting the system and setting it up in RAID 0 trim.

The tests we reran are: SiSoft Sandra 2004 Pro, Business Winstone 2004, Content Creation 2004, Code Creatures, Comanche 4, AquaMark 3, Serious Sam: The Second Encounter, Unreal Tournament 2003, Quake III and Return to Castle Wolfenstein (Checkpoint Demo).  All synthetic and gaming benchmarks were patched with the most recent updates available at the time of this writing.  Our aim here is to give you some idea of how much performance there is to be had here.   All game tests were run at 1024x768 resolution.  The Hard|OCP's UT2003 benchmarking program and the Guru3D's Quake III benchmarking program were used in measuring.  All tests are the result of five runs per bench with the highest and lowest scores being thrown out.  The remaining three scores are averaged and that is what you see here.

Test Bed

Results

With the workloads balanced between the two disks, Sandra 2004 Pro's File System Bench was no surprise to us at all. 

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