Sunday, February 3, 2008

Hard Drive RAID Explained

Hard Drive RAID
No matter how fast your processor runs, or how big your memory is, if your hard drive can’t keep up with the speed, you are still stuck with a slow system. A simple way to boost up the speed of the hard drive is to use two or more identical drives and set them up in a RAID setting.

RAID is the acronym for Redundant Array of Inexpensive Disks. It is a method that utilizes multiple identical hard drives to exceed the performance of a larger and more expensive hard drive.

There are several forms of RAID, but the one that can give you the best performance boost is RAID 0, also known as Disk Striping.

What RAID 0 does is simply dividing the data evenly between two or more drives so that the workload is spread out among the drives. Instead of one hard drive doing all the work seeking and finding information, copying and moving it, there are two or more drives now sharing the workload.

In RAID 0 setup, a file is divided into many small parts (by default, each part is of size 128Kb). When the system writes data to a two drives setup, it will write the first part to the first drive, the second part to the second drive, the third part to the first drive, fourth part to the second drive and so on until the entire contents of the file have been written. If there are more than two drives, the data writing will be split among the drives evenly.

By utilizing multiple drives, the system can now write and retrieve data at a much faster speed. A two drives RAID 0 setup can increase speed up to 25% while a three drives setup can boost speed about 33%.


While using RAID 0, it is best to use two identical hard drive of the same storage size. Keeping in mind that the workload is being balanced, the computer can only deal with data as big as the smaller hard drive. If you have an 80 GB and a 120 GB drive in RAID 0, the computer can only treat them as two 80 GB drives, ignoring the extra 40 GB of space on drive two. You don’t want to spend money on storage size that you can’t use.

A drawback to RAID 0 is that if any one drive happens to crash, all your data are lost. If you value your data, you can include RAID 1 in your setup.

RAID 1, also known as mirroring, provides the backup feature for your hard drive. When two hard drives are set up in RAID 1, the exact data are written to the two hard drives. One hard drive is use for operation while the other hard drive serves as a backup. If the main hard drive is to fail, you still have the second hard drive to fall back on. To achieve RAID 1, you need to have two identical hard drive operating at the same time (for RAID 0, it is not necessary). 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 only 80 GB of storage rather than 160 GB.

RAID 10 (or RAID 0+1) is the integration of both RAID 0 and 1. By using 4 identical hard drives, two in RAID 0 while another two in RAID 1, you can achieve both speed and stability. While this is really the ideal configuration, the cost of buying two extra hard drives that cannot be used at all may be a price too high for some to pay. Based on your needs, you may want to judge for yourself if you want to go for RAID 0 or RAID 10 setup.

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