Posted by Paul Stokes
RAID stands for redundant array of independent disks and provides an increase in storage reliability due to its redundancy of back up. RAID combines two or more hard drives into a single stand alone unit. Multiple disks set up as a RAID are considered to be in a RAID array. All data that is stored is distributed across multiple discs in the array but is seen by the operating system as one stand alone disk.
RAID systems utilize three key concepts, mirroring, striping, and error correction.
Mirroring is when identical data is contained on multiple disks. Mirroring can speed up reading because the information can be retrieved from more than one spot. Consequently mirroring can slow down writing when correct data must be confirmed in multiple locations.
Striping is when blocks of data are split across multiple disks. This is used primarily for increasing performance. Since the data is written in blocks to different disks it allows the data to be reconstructed from multiple disks faster than a single disk can process the same data.
Error correction is when redundant parity data is stored so problems can be detected and possibly repaired. This process generally slows performance since the data needs to be read from multiple places as well as be compared for consistency.
RAID systems will use one or more of these key concepts to protect data. These concepts are used on various combinations to improve reliability and increase the availability of data, protecting important data in the event of hardware failure, and sometimes to increase the speed of data input and output.
RAID in most cases should not be considered back up. The goal of RAID is to prevent you from having to retrieve your backups and avoid downtime. RAID systems with redundancy can avoid interruption in the event one or possibly more disks in the array should fail. Once a failure of a disk occurs, that disk is replaced and the array will automatically rebuild while the system continues to operate normally. In some cases the system may need to be shut down during a disk swap. If it’s important that your system stay running you will need to make sure the RAID you set up supports hot swapping. This allows drives to be replaced without powering down the RAID.