Redundant Array of Inexpensive Disks
From Unofficial BOINC Wiki
This is a structured collection of Disk Drives that are configured and controlled in such a way that failures of one or more of the Disk Drives in the array will not result in the loss of data, performance, or both. In the simplest configuration two Disk Drives can be "Mirrored" and if one drive fails the data is safe because it is also available on the second Disk Drive. If the data is "Striped" across the two drives the speed of read and write operations increases, though now, if one drive fails you lose all of the data.
So, arrays can be combinations of Disk Drives that are "striped" and / or "mirrored" to achieve the desired level of speed and data protection. Other configurations are possible with RAID-5 being the most popular (after pure mirrors and striped configurations) with 3 or more disk drives being used as a single array with the data written to the disks in such a way that the failure of one Disk Drive will not result in loss of data. A RAID-5 Array is slower in performance than a typical mirror or stripe configuration but does allow slightly larger total disk space.
The use of "Hot Spare" Disks allows the system to begin automatic recovery operations by taking a disk in the array that is designated as the "Hot Spare" Disk and doing all of the required operations including the creation of the data on the Disk Drive so that the array is again configured so that the loss of data cannot occur. All of this is automatic and all the operators have to do is to remove the failed disk drive and replace it with a new disk drive and insert it into the RAID Array.
The use of RAID techniques improves system availability and speed, depending on the mix of RAID Levels and the physical Disk Drives. The use of RAID-5 and Mirroring adds to availability with a decrease in the Mean Time Between Failures because of the increase of system complexity.
- Redundant Array of Independent Disks