| Software RAID |
Hardware RAID |
External RAID |
| Included in the OS such as Windows, Netware, and Linux. All RAID functions are handled by the CPU which can shag it out rather quickly for other jobs |
Processor-intensive RAID operations are offloaded from the CPU to enhance performance. |
Connects to the server via a standard controller. RAID functions are performed on a microprocessor located on the external RAID controller independent of the host. |
| Features |
Features |
Features |
| Low price
No special controller |
Data protection and performance benefits
More robust fault-tolerant features and increased performance versus software-based RAID. |
OS independent
Build super high-capacity storage systems for high-end servers. |
RAID
Level
|
Minimum
Number
of Drives
|
Description
|
Strengths
|
Weaknesses
|
|
RAID 0
|
2
|
Data striping without redundancy
|
Highest performance
|
No data protection; One drive fails, all data is lost
|
| RAID 1 |
2 |
Disk mirroring |
Very high performance; Very high data protection; Very minimal penalty on write performance |
High cost; Because all data is duplicated, twice the storage capacity is required
|
| RAID 2 |
Not used in LAN |
No practical use |
Previously used for RAM error correction and in disk drives before the use of embedded error correction
|
No practical use; Same performance can be achieved by RAID 3 at lower cost |
| RAID 3 |
3 |
Byte-level data striping with dedicated parity drive |
Excellent performance for large, sequential data requests |
Not well-suited for transaction-oriented network applications; Single parity drive does not support multiple, simultaneous read and write requests
|
| RAID 4 |
3 (Not widely used) |
Block-level data striping with dedicated parity drive |
Data striping supports multiple simultaneous read requests |
Write requests suffer from same single parity-drive bottleneck as RAID 3; RAID 5 offers equal data protection and better performance at same cost
|
| RAID 5 |
3 |
Block-level data striping with distributed parity |
Best cost/performance for transaction-oriented networks; Very high performance, very high data protection; Supports multiple simultaneous reads and writes; Can also be optimized for large, sequential requests
|
Write performance is slower than RAID 0 or RAID 1 |
| RAID 0/1 |
4 |
Combination of RAID 0 (data striping) and RAID 1 (mirroring) |
Highest performance, highest data protection (can tolerate multiple drive failures) |
High cost; Because all data is duplicated, twice the storage capacity is required; Requires minimum of four drives |
| RAID 1/0 |
4 |
Combination of RAID 1 (mirroring) and; RAID 0 (data striping) |
Shares the same fault tolerance as RAID 1 (the basic mirror), but compliments fault tolerance with a striping mechanism with higher read rates |
High cost; Because all data is duplicated, twice the storage capacity is required; Requires minimum of four drives |
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