subject: What is RAID Data Storage? [print this page] What is RAID Data Storage? What is RAID Data Storage?
The term RAID is an acronym for Redundant Array of Independent Disks. It's a strategy for improving the safety and reliability of storing data by combining multiple hard disk drives into a single logical unit. The advantage of a RAID system lies in its increased redundancy. That is, since the data is stored on several different hard drives, it's less likely that it will be lost due to hard drive failure. If one drive fails, as occasionally happens, your data should still be safe, since it's stored on more than one drive.
RAID Data Storage
The RAID concept was first conceptualized in 1987 by researchers at the University of California, Berkeley. The term is now used to refer to any data storage system that can copy and divide data files among two or more disk drives. Despite the fact that multiple disk drives are used, the computer's operating system addresses the entire system as if it were a single drive.
The goals of this system are twofold:
1. To increase the reliability of your data.
Storing your important data on two or more disks makes less vulnerable to losing it due to a drive failure.
2. Increased input/output performance.
Multiple drives allow you increased storage and faster access to your files.
RAID systems are appropriate when you have large amounts of data to store or when the information you're storing is important enough that you want a readily accessible backup.
RAID Techniques
There are three fundamental RAID techniques that are used by the various RAID levels to a greater or lesser degree. The three types are mirroring, striping and striping with parity.
Mirroring
Mirroring is simply storing the same data in two separate hard drives. The advantage of this is that if one drive fails, you have the data stored on another drive so you don't lose it. It can also process two data read requests at the same time and therefore access data more quickly than a single drive could.
Striping
This is the process of distributing data across several hard drives. Striping works very well for single tasks, but is not as fast as mirroring for multiple tasks. Striping doesn't provide redundancy, so if one drive fails, the entire system fails. As a result, striping is usually used in conjunction with mirroring or parity so that it has some level of fault tolerance.
Striping with Parity
Striping with parity reduces the storage capacity somewhat compared to striping alone, but it adds fault tolerance. Parity data allows data to be reconstructed if one or more of the drives in the array fail.
RAID Levels
There are different levels of RAID, each providing varying levels of performance standards and protection from data loss.
RAID 0
RAID 0 provides added storage, but doesn't store the information on more than one drive, so a single drive failure can wipe out the entire system. This type of system is even more prone to failure that a single drive. With more than one drive connected, (any one of which could cause the entire system to crash), the likelihood of failure is increased significantly.
RAID 1
RAID 1 systems write all the data onto multiple disks. This gives you some fault tolerance since the failure of one drive does not affect any of the other drives in the system and as long as you have at least one working drive, your data is safe.
RAID 2
RAID 2 allows for all disk spindle rotation to be synchronized, and each bit in the sequence is stored on a different disk. This allows you to transfer data at a substantially increased rate.
RAID 3
RAID 3 also synchronizes all spindle rotation (like in a RAID 2 setup) and allows each byte of data to be stored on a different disk. This allows extremely high data transfer rates.
RAID 4
This setup keeps all parity data on a single disk and can cause a slower performance level due to data bottlenecks.
RAID 5
A RAID 5 setup distributes parity information to multiple disks along with the data. This array can withstand the loss of a single disk without crashing the system, although a drive failure will cause significantly reduced performance until the damaged drive is replaced.
RAID 6
This is similar to RAID 5 but allows for up to two disks to fail without crashing the system.
The type of RAID array that you use depends on the amount of data you need to store and the level of fault tolerance that you require. Levels 0, 2 and 3 provide better performance, while levels 1, 4, 5 and 6 provide better protection against data loss. The decision of priority between data security and performance is paramount in choosing which setup will work for you. Speaking with a data recovery company about the pros and cons of each system will help you make the decision that best meets your needs in protecting your data.
