Features at RAID levels

Source: Internet
Author: User
Tags bitwise


Redundant Arrays of inexpensive Disks(redundant array of inexpensive disks)

Independent Redundant Array of independent disks

Berkeley:A case for redundentarrays of inexpensive Disks RAID

Multiple independent physical hard disks are combined in different ways to form a virtual hard disk to improve performance and redundancy;

What problems can be solved:

Improve IO Capability

multiple disk parallel read and write to achieve; RAID Controller Advanced products have dedicated raid memory, independent power supply;

Increased durability

Disk redundancy to achieve;

the benefits of RAID

RAID has the advantage of capacity and management

Easy and flexible capacity expansion;

"Virtualization" makes manageability greatly enhanced;

performance Benefits of RAID

"Disk chunking" technology brings performance improvement;

The benefits of RAID in reliability and availability

The reliability is improved by redundancy technology and hot-standby and heat exchange.

how the RAID is implemented:

An external disk array, with an expansion card that provides the ability to fit, the expansion card is called Adapter Adapter;

Internal-Connection RAID: Motherboard integrated RAID controller

Software RAID:

RAID level: Used only to identify disk organization forms

of different RAID level, multiple disk organizations work together in a different way;

Different storage performance

RAID-0:0 -level, striped reel,strip;

RAID-1:1 levels, mirrored volumes,mirror;






The RAID mechanism also divides the files into blocks, where the blocks are called chunk, and thestorage format is to store the data in different hard drives .

How the RAID-0 works

is to distribute the data evenly on the individual disks of the array in the form of strips;

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Number of disks: Minimum of 2 ;

Advantages: Read, write performance improvement, there is no verification, not too much CPU resources, design, use and configuration is relatively simple;

Disadvantage: No redundancy ability, can not be used for high data security requirements of the environment;

free Space: N(number of hard drives)*min(s1,s2 ... depending on the space of the smallest hard disk)

Applicable areas: Video generation and editing, graphics editing, and other needs of large transmission bandwidth operation;

RAID-1 Working principle:

Redundant copies of the data on the virtual disk, on the member disk, in the form of a mirrored redundancy;

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Number of disks: Minimum 2 ,2n ,n greater than or equal to 1

Advantages: Read performance improvement, write performance decreased slightly, with 100% data Redundancy, provide the highest data security guarantee theoretically can achieve 2 times the Reading efficiency design and use is simpler;

disadvantage: The cost is big, the space utilization is only 50%, the writing performance aspect is not very important;

Have redundancy capability

free space:1*min(S1,S2 ... Determined by the minimum hard disk space)

Applicable field: Finance, finance and other high-availability, high-security data storage environment;


Using checksum redundancy

Scatter data into bits or blocks, add Hamming codes, and write to each disk in the disk array at intervals

The addresses on the member disks are the same

The way to use parallel access

It costs a lot and is expensive

How the RAID-3 works

The data blocks are divided into smaller chunks, which are transferred to each member disk in parallel, and the XOR checksum data is stored on the dedicated check disk;

XOR algorithm: XOR

The same is false, the difference is true

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Number of disks: Minimum of 3

Advantages: Read and write performance is good, when the disk is damaged, the overall throughput of small impact, reduce the cost;

Disadvantage: Controller design is complex, using parallel access mode, spindle synchronization throughput does not improve, check disk write performance bottleneck;

Applicable areas: Video generation and image, video editing, etc., requiring high throughput of the application environment;


minimum 3 drives required;

data cross-stored in 2 hard drives, and then by the first 3 hard disk storage data verification code;

The check code is the value of the chunk block in 2 hard disk which is different or calculated by the bitwise;

1 of the hard drive does not affect the file data read and write operations, the data can be restored, but it is somewhat slow, even if the bad 1 hard disk still continue to work online, called the downgrade mode, the data is not guaranteed, the risk is greater , so immediately replace the bad hard disk with a new hard drive, tentative business, with 2 free disk to calculate, bitwise verify the recovery of data to the new hard disk, when all the data is restored to the new hard disk, you can continue to work normally, but in case the recovery process is also risky;

RAID4 also has an inherent disadvantage: the use of a single disk as a store check code, regardless of the front of the disk access data, the calibration disk must be accessed, that is, centralized check code check disk access pressure is too large, it is easy to cause performance bottlenecks; Therefore, early detection of bad disk damage, can be replaced early; 1 new hard disks as spare disks.

XOR operation, store check code:

For example:1101,0110 bitwise check, CHECKSUM code:1011

How the RAID-5 works

Using the independent Access array method, the calibration information is distributed evenly to each disk of the array;

relative to RAID-4 The check code is stored on a hard disk, and the RAID-5 is the 3 disk rotation for storage check code. The order of the left symmetry that the check code stores each disk is first in the first 2 pieces of inventory data, the first 3 block inventory check code, and so on, and so on, right symmetry opposite.

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Number of disks: Minimum of 3

Advantages: High reading performance, medium write performance, check the distribution of information access to avoid the bottleneck of writing operations;

Disadvantage: Controller design is complex, the process of disk reconstruction is more complicated;

free space: ( N-1)*min(S1,S2,... the smallest of these spaces)

fault tolerance:1 disks

applicable domain: File server,email server,Web Server and other environment, database application;

RAID-6: Use 2 disk to do check disk, check the code to save two times;

Read and write performance improvement;

free space: ( N-2)*min(S1,S2,... minimum space)

Fault tolerance:2 disks;

minimum number of disks:4,4+

combine different levels of Raid

combine different levels of Purpose of RAID

from RAID0 to RAID6, different levels of RAID in performance, redundancy, price and other aspects of the different transfer of the compromise;

Key Introduction:


How the RAID-10 works

RAID10 combined with RAID1 and RAID0, first mirror, then strip;

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Number of disks: Minimum 4 ,2n ,n greater than or equal to 2;

Advantages: High reading performance, good write performance, good data security, allowing simultaneous N disk failure;

Disadvantage: The utilization rate is only 50%, the cost is big;

free Space: N*min(S1,S2,... where the minimum space)/2;

Fault tolerance: Each group of images can only be broken one piece;

application area: Used in database applications requiring high availability and high security;


into two groups first . RAID-0, and then make the composition of the RAID-0 into RAID-1,do not conform to the common methods, each group has a bad hard disk is likely to be large;

How the RAID-50 works

is a the combination of RAID5 and RAID0, first realize RAID5, and then strip,(first do RAID-5 in doing RAID-0, at least 6 plates, Each group allowed bad 1 disk, space utilization flexibility),RAID7(private technology of a company, actually file server)

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Number of disks: Minimum of 6 ;

Pros: Ratio RAID5 has a better reading performance, than the same capacity of the RAID5 reconstruction time is shorter, can allow N disk simultaneous failure;

Disadvantages: Complex design, more difficult to achieve; failure of two disks in the RAID5 group will result in the entire array being invalidated;

Applicable domain: Large database server, application server, file server and other applications;

JBOD:Just a Bunch ofdisks

Combine multiple disk space into one large contiguous space for use;

free space:sum(s1+s2+,... The sum of disk space)

Common RAID level comparisons:RAID-0,RAID-1,RAID-5,RAID-10,RAID-50,JBOD

RAID-0 the best performance;

RAID-1 redundancy is highest;

The same available capacity, RAID-1 and RAID-10 have the highest overhead;

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Features at RAID levels

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