Why does RAID make the hard drive run faster?

[EarthBrain]

O.K....I am a newbie at this and have never set my hard drives to RAID. I have two 150 GB WD velociraptors but I have them set up as two separate drives.

Why does RAID make the hard drive run faster? I thought that the purpose of RAID is to have data stored in the drives in an identical manner so that if one of the drive stop working, then you still have the other drive as a back up and all of the informations will not be lost.

It kinds of counter-intuitive to think that running two drives and accessing data and writing data on the "two" drives would be faster. I thought that it would slower to "do things" on two drives because you have to work twice as hard.

Strange....

 

[Yoda4561]

there are different kinds of raid, most are for data redundancy, all of them increase read speeds. Raid 0 is the one most talked about here because it's the one with the greatest performance increase, however it has no data redundancy whatsoever. It works by splitting data into different parts across multiple drives. With a good raid controller this means that it can read from and write too all of those drives as if they were a single drive, but no longer limited by the speed of a single drive. Now your read and write speeds are multiplied by the number of drives in the array, until the controller runs out of bandwidth. Different drives and raid controllers act differently, some fall short of that ideal, others somehow seem to be more than twice as fast in some benchmarks.

Edit: It's not counter intuitive at all. Instead of thinking "two drives = more work" Think, "two drives= half as much work for each drive".

 

[DeathFromBelow]

Yoda4561 summed it up pretty well. Keep in mind that using RAID 0 won't dramatically improve performance, you probably wouldn't even notice most of the time. The nice thing about it is you would have "one" big 300 GB drive rather than two seperate 150 GB drives.

It also bears repeating that RAID 0 provides no redundancy. If one drive fails you lose everything on the array. Anything important stored on a RAID 0 array should be backed up to another drive.