Standard Technology - What is RAID?
WHAT IS RAID?
RAID stands for Redundant Array of Independent (or Inexpensive) Disks.
The basic idea of RAID is to combine multiple small, inexpensive disk drives into an array of disk drives which performs better than a large, expensive drive. The array of drives appears to the computer as a single drive.
Disk arrays can be made fault-tolerant by redundantly storing data (i.e. duplicating all or part of the data stored over the drives). If one of the disks fails, the data is still preserved over the remaining healthy disks. There are several forms of RAID, most provide disk fault-tolerance and each form offers different trade-offs in features and performance.
Two of the More Common, Redundant RAID Options:
RAID-1: Mirroring
RAID-1 provides fault tolerance but does not improve performance or provide excessive capacity. Multiple drives are created identically, meaning the data is saved to all drives, not just one. In the case of drive failure, there will be an identical drive to replace the faulty one.
| Disk 1 | Disk 2 |
|---|---|
| Data Bit 1 | Data Bit 1 |
| Data Bit 2 | Data Bit 2 |
| Data Bit 3 | Data Bit 3 |
RAID-5:
RAID-5 requires at least 3 drives. Data is split into blocks and stored over all the drives. Parity data is distributed amongst all of the drives and is used to regenerate lost data. In the case of a drive failure, RAID-5 will be able to regenerate the missing data from the parity data remaining on the healthy drives.
| Disk 1 | Disk 2 | Disk 3 |
|---|---|---|
| Data Block 1 | Data Block 2 | Parity for 1 & 2 |
| Data Block 3 | Parity for 3 & 4 | Data Block 4 |
| Parity for 5 & 6 | Data Block 5 | Data Block 6 |
WHICH CONFIGURATION MODE SHOULD I USE?
The configuration mode you choose depends on your needs:
STORAGE SPACE
Standard: Not using RAID permits the use of the complete capacity of all drives. Each drive is seen as its own, independent drive, but there is no fault-tolerance. If a drive fails there is no way of replacing the lost data on that drive.
RAID-0: This option uses all drives as an array but it is not redundant. This option also permits the use of the complete capacity of the drives, but the drives are seen as one massive drive.
The advantage over the standard configuration is that now the max capacity for storing large data files is the capacity of all drives, as opposed to the max capacity of a single drive. Users are not required to manage which drive they place their data on.
The disadvantage, however, is that it offers no fault-tolerance and if one of the disks fails, the data on all of your drives is lost.
HIGHEST FAULT-TOLERANCE
Mirroring: RAID-1 mirrors the data completely onto all of the disks providing multiple copies of all the data. However, this reduces your capacity to the size of a single disk.
FAULT-TOLERANCE & TOP PERFORMANCE
RAID-5: RAID-5 offers fault-tolerance in conjunction with high performance and large capacity. If one disk fails, the data is safe, but if two or more disks fail the data is lost. For most users, this is the recommended RAID mode used on TeraStations because it provides both redundancy and massive storage capacityTeraStation™.
Learn more about Buffalo Network Storage solutions supporting RAID: LinkStation™ and TeraStation™.
