RAID Level 2

This RAID level interleaves the data across multiple hard drives with parity information created using a Hamming code. The Hamming code detects errors that occur and determines which part is in error.

RAID Level 2 specifies 39 hard drives with 32 drives for actual data storage and 7 drives dedicated to error recovery coding. This RAID level is not used in practice.
 

RAID Levels 3 & 4

These two RAID levels stripe data across multiple drives and write parity to a dedicated drive. Level 3 is typically implemented at the BYTE level while Level 4 is typically implemented at the BLOCK level.

These Levels combine the performance of a RAID 0 array with data redundancy. If a drive fails, the data can be restructured using data on the parity drive. RAID 3 and 4 are best suited for large transfer sizes and rates where data redundancy is important. The parity information is calculated during write time and can affect overall performance. Spare drives take over in the event of a drive failure.

Minimum number of hard drives : 3
 

RAID Level 6

RAID Level 6 creates a striped set with dual parity. It provides fault tolerance from two drive failures. Therefore, this RAID array can continue to operate with up to two failed drives. This feature makes larger RAID groups more practical, especially for high availability systems.

This becomes increasingly important because large-capacity drives lengthen the time needed to recover from the failure of a single drive. Single parity RAID levels are vulnerable to data loss until the failed drive is rebuilt. The larger the drive, the longer the rebuild. The dual parity feature gives you time to rebuild the array without the data being volatile while the failed drive is being recovered.

Minimum number of hard drives : 4
 

RAIDn

This is a proprietary RAID system which claims to exceed the capabilities of RAID Level 6.
 

RAID DP (Dual Parity)

This is very similar to RAID Level 6. The key difference is the parity is fixed. This RAID level is used in NAS storage bays.
 

Page

Topic

1

• Introduction
• Background

2

• RAID Types
• Software RAID
• Fake Hardware RAID

3

• Real Hardware RAID

4

• RAID Levels
• Common RAID Levels

5

• Uncommon RAID Levels

6

• Combined RAID Levels

7

• Special RAID Levels

8

• Hot Plug / Hot Swap
• Parting Words