What is RAID?
RAID (Redundant Array of Independent Disks) is a set of technology
standards for teaming disk drives to improve fault tolerance and
performance.
RAID Levels
| Level | Name |
|---|
| 0 | Striping |
| 1 | Mirroring |
| 2 | Parallel Access with Specialized Disks |
| 3 | Synchronous Access with Dedicated Parity Disk |
| 4 | Independent Access with Dedicated Parity Disk |
| 5 | Independent Access with Distributed Parity |
| 6 | Independent Access with Double Parity |
Choosing a RAID Level
Each RAID level represents a set of trade-offs between performance, redundancy, and cost.
RAID 0 -- Optimized for Performance
RAID 0 uses striping
to write data across multiple drives simultaneously. This means that
when you write a 5GB file across 5 drives, 1GB of data is written to
each drive. Parallel reading of data from multiple drives can have a
significant positive impact on performance.
The trade-off with RAID 0 is that if one of those drives fail, all of your data is lost and you must retore from backup.
RAID 0 is an excellent choice for cache servers, where the actual
data being stored is of little value, but performance is very important.
RAID 1 -- Optimized for Redundancy
RAID 1 uses mirroring
to write data to multiple drives. This means that when you write a
file, the file is actually written to multiple disks. If one of the disks
fails, you simply replace it and rebuild the mirror.
The tradeoff with RAID 1 is cost. With RAID 1, you must purchase double the amount of storage space that your data requires.
RAID 5 -- A Good Compromise
RAID 5 stripes data across multiple disks. RAID 5, however, adds a
parity check bit to the data. This slightly reduces available disk
capacity, but it also means that the RAID array continues to function
if a single disk fails. In the event of a disk failure, you simply
replace the failed disk and keep going.
The tradeoffs with RAID 5 are a small performance penalty in write operations and a slight decrease in usabable storage space.
RAID 6 -- Better Redundancy
RAID 6 stripes data across multiple disks. RAID 5, however, adds double
parity check bits to the data. This slightly reduces available disk
capacity, but it also means that the RAID array continues to function
if a two disk fails. In the event of two disks failure, you simply
replace the failed disks and keep going.
RAID 1+0 -- Optimize for Performance and Redundancy
RAID 1+0 combines the performance of RAID 0 with the redundancy of RAID 1.
To build a RAID 1+0 array, you first build a set of RAID 1 mirrored
disks and you then combine these disk sets in a RAID 0 striped array.
A RAID 1+0 array can survive the loss of one disk from each mirrored
pair. RAID 1+0 cannot survive the loss of two disks in the same
mirrored pair.
For more information, please also refer to http://en.wikipedia.org/wiki/RAID.
