Summary: RAID uses multiple hard drives to "look like" a single drive increasing either speed, reliability or both. RAID 0 is a configuration with serious risk.
I regularly get questions from people experiencing problems with their hard drives, and one configuration I've seen more and more of is something called "RAID 0". It's such a bad idea, in my opinion, I wanted to draw attention to it and detail why.
Of course that means I also need to touch on just what RAID is, since other variations of RAID are actually quite valuable.
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"RAID" stands for "Redundant Array of Inexpensive Disks", and refers to several different ways to use multiple hard drives to either increase performance, reliability or both. RAID is typically transparent to you or the operating system, other than the fact that there is a dedicated piece of hardware, known as a RAID controller, that manages the distribution of data across the drives.
Various standard configurations of RAID drives, typically referred to as "RAID arrays", have been labeled with numbers to differentiate the differing arrangements.
RAID 0 uses two (or more) drives to increase performance.
The approach is this: when you write data to the logical (say, "C:") drive, the data is interweaved in some way such that half of it is written to one physical drive, and half on the other. Effectively, this doubles the speed of your hard disk, since the computer can essentially be writing to both at the same time, instead of writing the same amount of data in two steps to a single drive.
Sounds like a nifty approach, right? You get the same amount of space as you would with two individual drives, but you get it twice as fast.
The problem is that you get twice as much of something else as well: chance of failure and catastrophic data loss.
If one drive has, say, a 1 in 1,000 chance of failure, then two drives have a 2 in 1,000 chance.
Now, if you have two separate drives you still have that same 2 in 1,000 chance of one of them failing - but all you lose is what's on that one drive that fails. In a RAID 0 configuration, you've doubled your chances of failure, and when failure happens, all of your data on both drives is lost.
Think of it this way: if we take a simple sentence like:
RAID 0 configurations are a bad idea.
and sliced it in half such that every other letter was "on alternate drives", this might be what appears on each drive:
Drive 1: R I o f g r t o s a e a b d i e .
Drive 2: A D 0 c n i u a i n r a d a
Together they're easy (and quick!) to combine into the original sentence. Take away either one and the other is so much gibberish.
RAID 0 is valuable as a speed enhancement only if you're willing to take double the risk of failure. That means either that it's OK if the failure happens and you lose the data, or you're conscientious about making sure that it's backed up regularly and thoroughly.
I'm not really sure why I'm seeing this configuration more and more, but it does concern me that people are taking it on without understanding the risks.
What's frustrating, in part, is that once you have a RAID controller anyway, with the addition of a third (inexpensive) drive you can get all that speed as well as fault tolerance using different RAID configuration.
Using RAID 5, a third drive contains "parity" information - kind of the "C" in an "A + B = C" type of equation - lose any of A, B or C and it can be recalculated from the other two. In the world of hard disk drives, that means a drive can fail completely and your system continues to operate while the disk is replaced. RAID controllers often include "hot swap" ability, so that could even be literal: the drive could be replaced without stopping or restarting the system.
That's just one example - RAID as a concept actually includes several different arrangements that you can use to balance performance, fault tolerance and risk.
Just make sure that if you're using RAID 0, you know what you're getting into.
Related:
Your hard disk is more likely to fail than you think. A recently released report from Google has some disturbing information.
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How do I backup my computer? Backing up your computer is an important step to avoiding data loss. We'll look at what it is, and give a suggestion for average users.
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How should I keep my hard drive clean and working at its best? Hard drives can last a long time if properly cared for. More often than not issues result not from hardware, but from easily managed data and software.
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What is disk partitioning? Partitions are ways of treating a single hard disk as if it were many. We'll look at why, how and when you might want to partition your hard drive.
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Wikipedia: RAID - a nice overview of the various configurations.
Article C3806 - July 12, 2009
I use RAID 0 for 4 years and I am very pleased with the performance (speed) BUT I use a external HDD for weekly backup. If you think only at bad things you do not dare to cross the street.
Posted by: Corneliu Coterbic at July 14, 2009 1:05 PMYour analysis of increasing your failure rate from 1 out 1000 to 2 out of 1000 is even worse. Using an MYBF calculation, the failure chances increase to much more than 2 out of 1000. But your thought, as usual, is great.
15-Jul-2009
Posted by: C. W. Joiner at July 14, 2009 2:45 PM
RAID 0 is NOT a bad idea if you need the speed and if you have fault tolerance system.
Posted by: Chris Hingee at July 14, 2009 5:03 PMIf I needed RAID 0, I would also mirror the drives. This would double the cost of hard drives, but it is worth protecting your data.
Not really RAID related but addressing a comment by Corneliu. I'm impressed that at least some people bother to do a backup. However, I do a lot of work in one day; six to seven times that in one week. I can't afford to lose a week's work on the day before doing a weekly backup. That's why I do a daily backup - with a sensible protocol and good backup software, it literally takes less than 10 minutes to do an incremental backup.
For the record, I use RAID 5.
Finally Leo, you mentioned a "piece of hardware" - a RAID controller - which can be either a discrete card OR built in to the Mother Board. However (and I guess you omitted it to avoid confusion) there is also Software RAID if your readers care to investigate.
Posted by: David at July 14, 2009 6:20 PMThe "software" raid you are talking about David can be created using windows dynamic disks where disk manager in windows can create stripped partitions/etc. I honestly dont like dynamic disks.. I rather have it done the "right way" during the boot process so partitioning tools can work from bootable CDs, etc, otherwise if windows fails, the stripped partitions might be in trouble...
I honestly like the idea of RAID5 or RAID 1+0.
RAID5 requires at least 3 drives to work and its basically mirroring between 3 drives with a parity section on each drive with information from at least 1 other drive dedicated. If 1 drive dies, the RAID will continue to work flawlessly with a small performance drop (still faster than just 1 drive). If a 2nd drive dies, your in trouble. This raid is n-1 drives in disk space.
RAID 1+0 would require at least 4 drives and is most definitely the fastest and most protected. It would be n-2 drives in disk space, but this RAID would only fail if all the drives fail on a single strip (highly unlikely).
Posted by: Chris Awad at July 14, 2009 7:27 PMLike RAID 5? Don't forget your MOTHERBOARD can fail, too! If it does (a very frequent occurance with the recent rash of Bad Capacitors) you'll need to go out and buy another Motherboard with the same RAID CONTROLLER to recover your Data. I use only RAID 1, so I can remove a Mirrored Hard Drive and read it on any Windows PC.
Posted by: SalemCat at July 15, 2009 11:47 AMHow do I get rid of RAID? I keep getting a message that it has stopped working. I do not want it.
16-Jul-2009
Posted by: Leo Hasbrouck at July 15, 2009 4:23 PM
As a tech, I saw one of the big mistakes that a computer company can do and it was the Now gone MPC computer. In the end I got some PCs from them that had Vista on them and my company wanted XP on them. Well I tried to install the XP software and it would not. I emailed their tech support and after the run around one of their final techs said the RAID in the BIOS was on. I went in and turned it off and was able to install XP. Now RAID is a bad thing when you have one drive. If you really need a RAid system in your house I hope your related to the edisons for your electric power. I know there are people out there running a server at their house, but ask why risk it all just to use RAID on either a server or a home PC. In the early days of RAID at companies you were risking allot I saw RAID not work I know these days they are much better and are working now. I've been working on computers for over 30 years and still don't see people keeping it simple. Home users with drives so cheap you can pick up a stand alone drive turn it off and on when you want, save time, save electric, and save money. If you have files save them there and then if you don't use the files then put them on a cd, dvd, or blue-ray disk. If your a a home computer user and your spouting I have a RAID on your home system then your just wasting your own time. Rule of Thumb RAID bad for home users, RAID good for Bussiness servers at companies. Drives are going to die and your going to have to replace them, same with motherboards, and other computer parts they don't last forever. Keep your computing simple thats what computing was supposed to be all about.
Posted by: Alan at July 17, 2009 6:22 AMI was always told RAID meant, "Redundant array of independent drives." Weird...
Posted by: Sandy Smith at July 25, 2009 8:53 PMYou are both sort of right, RAID stands for "Redundant Array of Independent Disks". It was "Redundant Array of Inexpensive Disks" but the companies that make RAID equipment did not like the word "Inexpensive" since it made RAID sound cheap. And Sandy is sort of right because "Drives" are also called disks. But I am still back in the time when URL stood for "Universal Resource Locator"
Posted by: Art at August 5, 2009 12:25 PM