RAID Levels Explained


RAID Capacity Large Data Transfers High I/O Rate Data Availability

Single Disk

Fixed 100%

Good

Good

Single drive MTBF

RAID 0

Excellent 100%

Very Good

Very Good

Poor * MTBF of drive

RAID 1

Moderate 50%

Good

Good

Good

RAID 3

Good – Very Good*

Very Good

Good

Good

RAID 5

Good – Very Good*

Good – Very Good*

Good

Good

RAID 6

Moderate – Good**

Very Good**

Good

Very Good

RAID 0+1

Moderate 50%

Good

Very Good

Good

RAID 10 (1+0)

Moderate 50%

Very Good

Very Good

Very Good

RAID 30 (3+0)

Good – Very Good*

Very Good

Excellent

Excellent

RAID 50 (5+0)

Good – Very Good*

Good – Very Good*

Excellent

Excellent

MTBF = Mean Time Between Failures
* dependant on the number of drives in the RAID (3 to 16).
** dependant on the number of drives in the RAID (5 to 16).

Raid 0

Striped Disk Array without Fault Tolerance
Offers no redundancy or fault tolerance, hence does not truly fit the “RAID” acronym. In level 0, data is striped across drives, resulting in higher data throughput. Since no redundant information is stored, performance is very good, but the failure of any disk in the array results in data loss. This level is commonly referred to as striping. Requires a minimum of 2 drives to implement.


 
Advantages

  • RAID 0 offers a very high level of performance for both read and write operations
  • No parity bit to generate
  • Maximum storage capacity used, no disk used
  • Easy to implement

Disadvantages

  • Not fault tolerant as no it is not a “true RAID”
  • A single drive failure will result in all data lost
  • Not recommend for mission critical systems

Application

  • Video Production and Editing
  • Image Editing
  • Pre-Press Applications
  • Ideal as a starter solution where high I/O performance is required more than file redundancy

 

Raid 1

Disk Mirroring & Duplexing
RAID 1 provides redundancy by writing all data to two or more drives. The performance of a level 1 array tends to be faster on reads and slower on writes compared to a single drive, but if either drive fails, no data is lost. This is a good entry-level redundant system, since only two drives are required; however, since one drive is used to store a duplicate of the data, the cost per megabyte is high. This level is commonly referred to as mirroring. Requires a minimum of 2 drives to implement.


 
Advantages

  • Extremely fault tolerant
  • No parity bit to generate
  • Utilises full disk capacity
  • Easy to implement

Disadvantages

  • Inefficient use of disk space
  • High disk overhead
  • Doubles number of writes

Application

  • Accounting
  • Payroll
  • Financial
  • Any application requiring very high availability

 

Raid 3

Parallel Transfer with Parity
RAID 3 provides redundancy by writing all data to three or more drives. This RAID 3 disk array provides excellent storage for video imaging, streaming, publishing applications or any system that requires large file block transfers. Requires a minimum of 3 drives to implement.

Advantages

  • Single dedicated parity disk
  • High read data rate
  • High write data rate
  • No performance degradation if drive fails
  • Best and worst case performance similar

Disadvantages

  • Inefficient with small file transfer

Application

  • Video Production and live streaming
  • Image Editing
  • Video Editing
  • Prepress Applications
  • Ideal for video streaming/processing that process large blocks and files sequentially.

 

Raid 5

Striping with dedicated parity drive
RAID 5 provides redundancy by writing data and parity information across three or more drives, thus increasing performance. The RAID 5 provides the best combination of disk array technology. Requires a minimum of 3 drives to implement.

Advantages

  • Best balance cost / performance / protection of any RAID system
  • Allows multiple simultaneous writes
  • High read data rate
  • Medium write data rate
  • Ideal for small write applications
  • Highly efficient

Disadvantages

  • Inefficient with large file transfer
  • Disk failure has an impact on performance

Application

  • File and Application servers
  • Database servers
  • Web, E-mail, and News servers
  • Intranet servers

 

Raid 6

Striping with double parity drive
RAID 6 is an evolution of RAID 5. RAID 6 uses double parity for additional fault tolerance. Like in RAID 5, data is striped at a block level across the disk sets while parity information is generated and written across the array. Now it’s possible for more than one drive to fail simultaneously, and the RAID will still operate. Requires a minimum of 4 drives to implement.

Advantages

  • Perfect solution for mission critical applications as it can sustain multiple drive failures

Disadvantages

  • Uses 2 drives for parity

Application

  • File and Application servers
  • Database servers
  • Web, E-mail, and News servers
  • Intranet servers
  • Transaction processing

 

Raid 0+1

Striping and Mirroring across multiple RAID levels
RAID 0+1 provides redundancy by writing all data to four or more drives. RAID 0+1 combines the benefits of RAID 0 and RAID 1. This offers both striping and mirroring with no parity generation. The RAID 0+1 also provides high performance and resilience to RAID 5. Requires a minimum of 4 drives to implement.

Advantages

  • No parity bit to generate
  • Easy to implement
  • Utilises full disk capacity
  • Higher performance than RAID 5

Disadvantages

  • Inefficient use of disk space
  • High disk overhead / Expensive
  • Expensive to deploy

Application

  • General File servers
  • Imaging applications
  • Medium size database applications

 

Raid 10 (1+0)

Mirroring and Striping across multiple RAID levels
RAID 10 provides very high performance and redundancy. Data is simultaneously mirrored and striped. Can under circumstances support multiple drive failures. Requires a minimum of 4 drives to implement


 

Advantages

  • Highly fault tolerant
  • High data availability
  • Very good read / write performance

Disadvantages

  • Very costly to implement
  • Drive spindles must be synchronised
  • Not very scaleable

Application

  • Where high performance and redundancy are critical

 

Raid 30 (3+0)

Striping across dedicated parity RAID systems
RAID 30 is also known as striping of dedicated parity arrays. It is a combination of RAID level 3 and RAID level 0. RAID 30 provides high data transfer rates, combined with high data reliability. RAID 30 is best implemented on two RAID 3 disk arrays with data striped across both disk arrays. RAID 30 breaks up data into smaller blocks, and then stripes the blocks of data to each RAID 3 raid set. RAID 3 breaks up data into smaller blocks, calculates parity by performing an Exclusive OR on the blocks, and then writes the blocks to all but one drive in the array. The parity bit is created using the Exclusive OR is then written to the last drive in each RAID 3 array. The size of each block is determined by the stripe size parameter, which is set when the RAID is created.

Advantages

  • Can sustain one to four drive failures while maintaining data integrity if each failed disk is in a different RAID 3 array.
  • Offers highest level of redundancy and performance

Disadvantages

  • Very costly to implement

Application

  • Data warehousing

 

Raid 50 (5+0)

Mirroring and Striping across multiple RAID levels
RAID 50 is a combination of RAID level 5 and RAID level 0. RAID 50 includes both parity and disk striping across multiple drives. RAID 50 is best implemented across two RAID 5 arrays with data striped across both disk arrays. RAID 50 breaks the data into smaller blocks, and then stripes the blocks to each RAID 5 raid set. RAID 5 breaks up data into smaller blocks, calculates parity by performing and Exclusive OR on the blocks, and then writes the blocks of data and parity to each drive in the array. The size of each block is determined by the stripe size parameter, which is set when the RAID is created.
Here is an example of RAID 51 which is a combination of RAID level 5 and RAID level 1.

Advantages

  • Can sustain one to four drive failures while maintaining data integrity if each failed disk is in a different RAID 5 array.
  • Offers highest level of redundancy and performance

Disadvantages

  • Very costly to implement
  • Drive spindles must be synchronised
  • Failure of two drives in one of the RAID 5 segments renders the whole array unusable

Application

  • Data warehousing

 

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