| Features | RAID 0 | RAID 1 | RAID 1E | RAID 5 | RAID 5EE |
| Minimum # Drives | 2 | 2 | 3 | 3 | 4 |
| Data Protection | No Protection | Single-drive failure | Single-drive failure | Single-drive failure | Single-drive failure |
| Read Performance | High | High | High | High | High |
| Write Performance | High | Medium | Medium | Low | Low |
| Read Performance (degraded) | N/A | Medium | High | Low | Low |
| Write Performance (degraded) | N/A | High | High | Low | Low |
| Capacity Utilization | 100% | 50% | 50% | 67% - 94% | 50% - 88% |
| Typical Applications | High End Workstations, data logging, real-time rendering, very transitory data | Operating System, transaction databases | Operating system, transaction databases | Data warehousing, web serving, archiving | Data warehousing, web serving, archiving |
| Features | RAID 6 | RAID 10 | RAID 50 | RAID 60 |
| Minimum # Drives | 4 | 4 | 6 | 8 |
| Data Protection | Two-drive failure | Up to one disk failure in each sub-array | Up to one disk failure in each sub-array | Up to two disk failure in each sub-array |
| Read Performance | High | High | High | High |
| Write Performance | Low | Medium | Medium | Medium |
| Read Performance (degraded) | Low | High | Medium | Medium |
| Write Performance (degraded) | Low | High | Medium | Low |
| Capacity Utilization | 50% - 88% | 50% | 67% - 94% | 50% - 88% |
| Typical Applications | Data archive, backup to disk, high availability solutions, servers with large capacity requirements | Fast databases, application servers | Large databases, file servers, application servers | Data archive, backup to disk, high availability solutions, servers with large capacity requirements |
Types of RAID
| Types of RAID | Software-Based | Hardware-Based | External Hardware |
| Description | Best used for large block applications such as data warehousing or video streaming. Also where servers have the available CPU cycles to manage the I/O intensive operations certain RAID levels require.
Included in the OS, such as Windows®, Netware, and Linux. All RAID functions are handled by the host CPU which can severely tax its ability to perform other computations. | Best used for small block applications such as transaction oriented databases and web servers.
Processor-intensive RAID operations are off-loaded from the host CPU to enhance performance.
Battery-back write back cache can dramatically increase performance without adding risk of data loss. | Connects to the server via a standard adapter. RAID functions are performed on a microprocessor located on the external RAID adapter independent of the host. |
| Advantages | Low price
Only requires a standard adapter | Data protection and performance benefits of RAID
More robust fault-tolerant features and increased performance versus software-based RAID | OS independent
Build high-capacity storage systems for highend servers |
RAID 0
RAID 0, also called striping, is a scheme where data is divided into
blocks and distributed across the drives in the array. This level does
not provide redundancy, so consequently it has the best overall
performance. For this reason, it is not suitable for mission critical
situations, but is best used in situations where improved performance is
the primary driver.
RAID 1
There are two implementations of RAID 1: mirroring and duplexing.
With both schemes, data is duplicated on a second disk. Mirroring uses a
single drive controller, while duplexing uses two controllers. In the
event of a single drive failure, data can be read or written from the
other drive, providing fault tolerance. And in the case of duplexing,
even a controller failure won't bring down the system. However, there
won't be any performance improvements, but instead, a potential decrease
in write performance.
RAID 5
RAID 5 is called striping with distributed parity. Data and parity or
error detection and correction code, is striped across three or more
drives. Parity is stored on a dedicated drive, which results in less
available storage space. If a drive fails, data can be recovered from
the remaining data blocks and the parity information. This level also
features improved read and write performance because data can be read or
written simultaneously across multiple drives.
RAID 0+1 (01)
This is the first of the hybrids, which simply combines other RAID
levels. RAID 0+1 (also called 01) mirrors and stripes data
simultaneously. Combining striping and mirror marries high performance
with fault tolerance, making this one of the most popular levels. Under
this scheme, two striped arrays are created, and one acts as the mirror
to the other. This requires a minimum of four drives.
RAID 1+0 (10)
With this RAID level, data is mirrored and striped simultaneously.
Most often, this is implemented with four drives, and one mirrored drive
set is striped. This provides even higher fault tolerance and
performance. RAID 10 differs from 01 in that things are reversed. Where
01 is a mirror of stripes, 10 is a stripe of mirrors.
