RAID is a technology that is used to increase the performance and reliability of data storage. The abbreviation stands for Redundant Array of Inexpensive Disks. There are different RAID levels, each optimized for a specific situation. This article covers the following RAID levels
- RAID 0-striping
- RAID 1-mirroring
- RAID 5-striping is with parity
- RAID 6–striping is with double parity
- RAID 10–combination of both mirroring and striping
The software to perform the RAID-functionality and control the drives can either be located on a separate controller card or it can simply be a driver. Some versions of Windows, such as Windows Server 2012 as well as Mac OS X, include software RAID functionality. RAID controllers cost more than pure software, but they ensure better performance, especially with RAID 5 and 6.
System data are split up into blocks that get written across all the drives in the array. This offers superior I/O performance and can be enhanced further by using multiple controllers.
- Excellent performance
- No redundancy
- The technology is easy to implement.
Disadvantage: Don’t use this for any critical system.
Data are stored twice by writing them to both the data drive and a mirror drive. If a drive fails, then the controller uses either the data drive or the mirror drive for data recovery and continues operation. You need at least 2 drives for a RAID 1 array.
- Excellent read speed and a write speed that is comparable to that of a single drive.
- Good performance and excellent redundancy
Disadvantage: The effective storage capacity is only half of the total drive capacity because all data get written twice.
This level provides better performance than mirroring as well as fault tolerance. With RAID 5, data and parity are striped across three or more disks. If a disk gets an error or starts to fail, then data is recreated from this distributed data and parity block automatically.
- Good redundancy
- Best cost effective option by providing both performance and redundancy. Use this for DB that is heavily read oriented. Write operations will be slow.
Disadvantage: This is complex technology. If one disk goes bad in an array of disks, then data is lost forever.
It is identical to RAID 5, but the parity data are written into two drives. That means it requires at least 4 drives and can withstand 2 drives simultaneously. The chances that two drives break down at exactly the same moment are of course very small.
- Read data transactions are very fast
- Used frequently in enterprises
Disadvantage: Write data transactions are slower than RAID 5 due to the additional parity data that have to be calculated.
It is a combination of RAID 1 and RAID 0 and is often known as RAID 1+0. It combines the mirroring of RAID 1 with the striping of RAID 0. This RAID level is highly utilized for database servers or any server that is performing many write operations.
- If something goes wrong with one of the disks in a RAID 10 configuration, the rebuild time is very fast
- This the BEST option for any mission critical applications
Disadvantage: Half of the storage capacity goes to mirroring when compared to RAID 5 or RAID 6 arrays, this is an expensive way to have redundancy.
Other RAID Levels: 2, 3, 4 and 7
These levels do exist but are not that common, but they are really variants of the main RAID configurations already mentioned above.