RAID 0, RAID 1, RAID 2,RAID 3, RAID 4,RAID 5, RAID 6,RAID 10 Explained with Diagrams

RAID stands for Redundant Array of Inexpensive (Independent) Disks.

On most situations you will be using one of the following four levels of RAIDs.

• RAID 0
• RAID 1
• RAID 2
• RAID 3
• RAID 4
• RAID 5
• RAID 6
• RAID 10 (also known as RAID 1+0)

This article explains the main difference between these raid levels along with an easy to understand diagram.

In all the diagrams mentioned below:

• A, B, C, D, E and F – represents blocks
• p1, p2, and p3 – represents parity

RAID LEVEL 0

Following are the key points to remember for RAID level 0.

• Minimum 2 disks.
• Excellent performance ( as blocks are striped ).
• No redundancy ( no mirror, no parity ).
• Don’t use this for any critical system.

RAID LEVEL 1

Following are the key points to remember for RAID level 1.

• Minimum 2 disks.
• Good performance ( no striping. no parity ).
• Excellent redundancy ( as blocks are mirrored ).

However there are several non-standard raids, which are not used except in some rare situations. It is good to know what they are.

This article explains with a simple diagram how RAID 2, RAID 3, RAID 4, and RAID 6 works.

RAID 2

• This uses bit level striping. i.e Instead of striping the blocks across the disks, it stripes the bits across the disks.
• In the above diagram b1, b2, b3 are bits. E1, E2, E3 are error correction codes.
• You need two groups of disks. One group of disks are used to write the data, another group is used to write the error correction codes.
• This uses Hamming error correction code (ECC), and stores this information in the redundancy disks.
• When data is written to the disks, it calculates the ECC code for the data on the fly, and stripes the data bits to the data-disks, and writes the ECC code to the redundancy disks.
• When data is read from the disks, it also reads the corresponding ECC code from the redundancy disks, and checks whether the data is consistent. If required, it makes appropriate corrections on the fly.
• This uses lot of disks and can be configured in different disk configuration. Some valid configurations are 1) 10 disks for data and 4 disks for ECC 2) 4 disks for data and 3 disks for ECC
• This is not used anymore. This is expensive and implementing it in a RAID controller is complex, and ECC is redundant now-a-days, as the hard disk themselves can do this.

RAID 3

• This uses byte level striping. i.e Instead of striping the blocks across the disks, it stripes the bits across the disks.
• In the above diagram B1, B2, B3 are bytes. p1, p2, p3 are parities.
• Uses multiple data disks, and a dedicated disk to store parity.
• The disks have to spin in sync to get to the data.
• Sequential read and write will have good performance.
• Random read and write will have worst performance.
• This is not commonly used.

RAID 4

• This uses block level striping.
• In the above diagram B1, B2, B3 are blocks. p1, p2, p3 are parities.
• Uses multiple data disks, and a dedicated disk to store parity.
• Minimum of 3 disks (2 disks for data and 1 for parity)
• Good random reads, as the data blocks are striped.
• Bad random writes, as for every write, it has to write to the single parity disk.
• It is somewhat similar to RAID 3 and 5, but little different.
• This is just like RAID 3 in having the dedicated parity disk, but this stripes blocks.
• This is just like RAID 5 in striping the blocks across the data disks, but this has only one parity disk.
• This is not commonly used.

RAID LEVEL 5

Following are the key points to remember for RAID level 5.

• Minimum 3 disks.
• Good performance ( as blocks are striped ).
• Good redundancy ( distributed parity ).
• Best cost effective option providing both performance and redundancy. Use this for DB that is heavily read oriented. Write operations will be slow.

RAID 6

• Just like RAID 5, this does block level striping. However, it uses dual parity.
• In the above diagram A, B, C are blocks. p1, p2, p3 are parities.
• This creates two parity blocks for each data block.
• Can handle two disk failure
• This RAID configuration is complex to implement in a RAID controller, as it has to calculate two parity data for each data block.

RAID LEVEL 10

Following are the key points to remember for RAID level 10.

• Minimum 4 disks.
• This is also called as “stripe of mirrors”
• Excellent redundancy ( as blocks are mirrored )
• Excellent performance ( as blocks are striped )
• If you can afford the dollar, this is the BEST option for any mission critical applications (especially databases).

Additional RAID Tutorials:

• RAID 2, RAID 3, RAID 4, RAID 6 Explained with Diagram
• RAID 10 Vs RAID 01 (RAID 1+0 Vs RAID 0+1)

What is RAID configuration in Windows

RAID Configuration

Learn about Intel RAID configuration. It includes all the RAID levels with diagram, very useful for to clear doubts for layman.

RAID Level 0 requires a minimum of 2 drives to implement
Characteristic & Advantages

RAID 0 implements a striped disk array, the data is broken down into blocks and each block is written to a separate disk drive.

I/O performance is greatly improved by spreading the I/O load across many channels and drives.

Best performance is achieved when data is striped across multiple controllers with only one drive per controller.

No parity calculation overhead is involved.Very simple design & Easy to implement.

Not a “True” RAID because it is NOT fault-tolerant

The failure of just one drive will result in all data in an array being lost &Should never be used in mission critical environments

Disadvantages

Not a “True” RAID because it is NOT fault-tolerant.

The failure of just one drive will result in all data in an array being lost

Should never be used in mission critical environments

For Highest performance, the controller must be able to perform two concurrent separate

Reads per mirrored pair or two duplicate Writes per mirrored pair. RAID Level 1 requires a minimum of 2 drives to implement.

Characteristic & Advantages

One Write or two reads possible per mirrored pair

Twice the Read transaction rate of single disks, same Write transaction rate as single disks

100% redundancy of data means no rebuild is necessary in case of a disk failure, just a copy to the replacement disk

Transfer rate per block is equal to that of a single disk & Under certain circumstances, RAID 1 can sustain multiple simultaneous drive failures

Simplest RAID storage subsystem design & Highest disk overhead of all RAID types (100%) – inefficient

Typically the RAID function is done by system software, loading the CPU/Server and possibly degrading throughput at high activity levels. Hardware implementation is strongly recommended

May not support hot swap of failed disk when implemented in “software”

Disadvantages

Highest disk overhead of all RAID types (100%) – inefficient

Typically, the RAID function is done by system software, loading the CPU/Server and possibly degrading throughput at high activity levels. Hardware implementation is strongly recommended

May not support hot swap of failed disk when implemented in “software”

Recommended Product

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

Each bit of data word is written to a data disk drive (4 in this example: 0 to 3). Each data word has  its Hamming Code ECC word recorded on the ECC disks. On Read, the ECC code verifies correct data or corrects single disk errors.

Characteristic & Advantages

“On the fly” data error correction

Extremely high data transfer rates possible

The higher the data transfer rate required, the better the ratio of data disks to ECC disks

Relatively simple controller design compared to RAID levels 3,4 & 5
Very high ratio of ECC disks to data disks with smaller word sizes – inefficient

Entry level cost very high – requires very high transfer rate requirement to justify

Transaction rate is equal to that of a single disk at best (with spindle synchronization)

No commercial implementations exist / not commercially viable

Disadvantages

Very high ratio of ECC disks to data disks with smaller word sizes – inefficient

Entry level cost very high – requires very high transfer rate requirement to justify

Transaction rate is equal to that of a single disk at best (with spindle synchronization)

No commercial implementations exist / not commercially viable

The data block is subdivided (“striped”) and written on the data disks. Stripe parity is generated on Writes, recorded on the parity disk and checked on Reads.

RAID Level 3 requires a minimum of 3 drives to implement

Characteristic & Advantages

Very high Read data transfer rate & Very high Write data transfer rate

Disk failure has an insignificant impact on throughput

Low ratio of ECC (Parity) disks to data disks means high efficiency

Disadvantages

Transaction rate equal to that of a single disk drive at best (if spindles are synchronized) Controller design is fairly complex

Very difficult and resource intensive to do as a “software” RAID

Recommended Application

• · Video Production and live streaming
• · Image Editing
• · Video Editing
• · Prepress Applications
• · Any application requiring high throughput

Each entire block is written onto a data disk. Parity for same rank blocks is generated on Writes,                               recorded on the parity disk and checked on Reads.

RAID Level 4 requires a minimum of 3 drives to implement

Characteristic & Advantages

Very high Read data transaction rate

Low ratio of ECC (Parity) disks to data disks means high efficiency

High aggregate Read transfer rate

Disadvantage

Quite complex controller design

Worst Write transaction rate and Write aggregate transfer rate

Difficult and inefficient data rebuild in the event of disk failure

Block Read transfer rate equal to that of a single disk

Each entire data block is written on a data disk; parity for blocks in the same rank is generated on Writes, recorded in a distributed location and checked on Reads.

RAID Level 5 requires a minimum of 3 drives to implement

Characteristic & Advantages

Highest Read data transaction rate

Medium Write data transaction rate

Low ratio of ECC (Parity) disks to data disks means high efficiency

Good aggregate transfer rate
Disadvantage

Disk failure has a medium impact on throughput

Most complex controller design

Difficult to rebuild in the event of a disk failure (as compared to RAID level 1)

Individual block data transfer rate same as single disk
Recommended Application

• File and Application servers
• Database servers
• Web, E-mail, and News servers
• Intranet servers
• Most versatile RAID level

Two independent parity computations must be used in order to provide protection against double disk failure. Two different algorithms are employed to achieve this purpose.

RAID Level 6 requires a minimum of 4 drives to implement

Characteristic & Advantages

RAID 6 is essentially an extension of RAID level 5 which allows for additional fault tolerance by using a second independent distributed parity scheme (dual parity)

Data is striped on a block level across a set of drives, just like in RAID 5, and a second set of parity is calculated and written across all the drives; RAID 6 provides for an extremely high data fault tolerance and can sustain multiple simultaneous drive failures

Perfect solution for mission critical applications

Disadvantage

More complex controller design

Controller overhead to compute parity addresses is extremely high

Write performance can be brought on par with RAID Level 5 by using a custom ASIC for computing Reed-Solomon parity

Requires N+2 drives to implement because of dual parity scheme

Recommended Application

• File and Application servers
• Database servers
• Web and E-mail servers
• Intranet servers
• · Excellent fault-tolerance with the lowest overhead

RAID Level 10 requires a minimum of 4 drives to implement
Characteristic & Advantages

RAID 10 is implemented as a striped array whose segments are RAID 1 arrays

RAID 10 has the same fault tolerance as RAID level 1

RAID 10 has the same overhead for fault-tolerance as mirroring alone

High I/O rates are achieved by striping RAID 1 segments

Under certain circumstances, RAID 10 array can sustain multiple simultaneous drive failures

Excellent solution for sites that would have otherwise gone with RAID 1 but need some additional performance boost
Disadvantage

Very expensive / High overhead

All drives must move in parallel to proper track lowering sustained performance

Very limited scalability at a very high inherent cost

Recommended Application

• Database server requiring high performance
  and fault tolerance

RAID Level 50 requires a minimum of 6 drives to implement

Characteristic & Advantages

RAID 50 should have been called “RAID 03″ because it was implemented as a striped (RAID level 0) array whose segments were RAID 3 arrays (during mid-90s)

Most current RAID 50 implementation is illustrated above

RAID 50 is more fault tolerant than RAID 5 but has twice the parity overhead

High data transfer rates are achieved thanks to its RAID 5 array segments

High I/O rates for small requests are achieved thanks to its RAID 0 striping

Maybe a good solution for sites who would have otherwise gone with RAID 5 but need some additional performance boost.
Disadvantages

Very expensive to implement

All disk spindles must be synchronized, which limits the choice of drives.

Failure of two drives in one of the RAID 5 segments renders the whole array unusable

RAID Level 0+1 requires a minimum of 4 drives to implement

Characteristic & Advantages

RAID 0+1 is implemented as a mirrored array whose segments are RAID 0 arrays

RAID 0+1 has the same fault tolerance as RAID level 5

RAID 0+1 has the same overhead for fault-tolerance as mirroring alone

High I/O rates are achieved thanks to multiple stripe segments

Excellent solution for sites that need high performance but are not concerned with achieving maximum reliability
Disadvantage

RAID 0+1 is NOT to be confused with RAID 10. A single drive failure will cause the whole array to become, in essence, a RAID Level 0 array

Very expensive / High overhead

All drives must move in parallel to proper track lowering sustained performance

Very limited scalability at a very high inherent cost

Recommended Application

• Imaging applications
• · General fileserver

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