RAID0, 1, 5, 10 detailed

A RAID definition
RAID (Redundant array of independent disk independent Redundant array) technology was proposed by the University of California, Berkeley, in 1987, initially to combine small, inexpensive disks in place of large expensive disks, while hoping that the disk will fail without damaging access to the data Development of a certain level of data protection technology. RAID is a redundant array of inexpensive disks that appear as a separate, large storage device under the operating system. RAID can give full play to the advantages of multiple hard drives, can increase the speed of the hard disk, increase capacity, provide fault-tolerant work to ensure data security, easy to manage the advantages of any one hard disk problems can continue to operate, not affected by the damage to the hard drive.

Second, the raid several modes of operation (only discusses RAID0,RAID1,RAID5,RAID10 these four kinds, these four kinds of comparison typical)
1, RAID0 (also known as stripe or striping--sub-bar)
That is, data stripping is a sub-strip technology. RAID 0 can connect multiple hard drives into a larger drive group, which can improve disk performance and throughput. RAID 0 has no redundancy or bug fixes, is low cost, requires at least two disks, and is generally only used if the data security requirements are not high.

Characteristics:

fault tolerance:	no	redundancy type:	no
	no	read performance:
random write performance:	high	continuous write performance:	high
The number of disks required:	just 2 or 2*n (this should be more than two drives)	usable capacity:	Total disk capacity
	trouble-free fast read and write, Requirements of the security is not high, such as form workstations.

How RAID 0 Works:

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Figure 1

1: The I/O data requests made by the system to a logical hard disk (RADI 0 disk group) consisting of three disks are translated into 3 operations, each of which corresponds to a physical hard disk. We can clearly see that by establishing RAID 0, the original sequence of data requests is dispersed across all three drives simultaneously.
In theory, the parallel operation of the three drives increases the disk read and write speed by 3 times times over the same time. However, due to the influence of bus bandwidth and other factors, the actual increase rate will certainly be lower than the theoretical value, but, the large amount of data parallel transmission and serial transmission comparison, the speed-up effect is obviously undoubtedly.
RAID 0 'sDisadvantagesis not to provide data redundancy, so once the user data is corrupted, the corrupted data will not be recovered.
RAID 0 with somefeatures, making it especially suitable for the areas of high performance requirements, but not too concerned about data security, such as the shape of workstations. For individual users, RAID 0 is also an excellent choice for improving hard disk storage performance.
The computer technology develops rapidly, but the hard drive transmission rate also becomes the performance bottleneck. What to do? The sophistication of IDE RAID technology allows us to easily build our own ultra-fast drives. In practical applications, the RAID 0 HDD array can be much faster than the normal IDE 7200-ATA 133 hard drives, today, on most high-end or player motherboards we can find a promise or highpoint RAID chip, and found that the amount they provide A few IDE interfaces outside. Yes, RAID is already in sight, are you willing to give up raid for our performance gains? The answer is, of course, negative!
Practical IDE RAID
RAID can be implemented by software or hardware. Like Windows 2000 can provide software RAID capabilities, but this need to consume a small CPU resources, reduce overall performance. The hardware implementation is generally implemented by the raid card, high-end SCSI RAID card has its own dedicated cache and I/O processor, but for home users this is obviously not affordable, after all, in order to achieve RAID to buy two or more HDD has been quite difficult. We also have a compromise approach to--ide RAID. Perhaps this is the easiest way for ordinary people to accept it. While IDE raid has a tradeoff between functionality and performance, ordinary users don't seem to care about low prices.
Why use RAID 0
RAID 0 requires at least two hard drives to be able to achieve, its capacity is the sum of the capacity of each hard disk that makes up the system, the capacity of these hard disks to be the same, in the Home IDE raid in general Cascade two hard drives, must use the same model of the same capacity of the hard disk. RAID 0 Mode writes data to the hard disk when the data is divided into two pieces of hard disk, read the data when the reverse, so that each hard disk as long as the burden of half of the data transmission task, the result is the increase in speed.

Implementation method:

(1), RAID 0 The simplest way (I don't think this is what it meant to be)
is the X block the same hard disk in the form of hardware through the Intelligent disk controller or the operating system of the disk driver in a software-series together, to form a separate logical drive, the capacity of a separate hard disk x times, when the computer data is written to each disk, when the space of a disk is exhausted, The data is automatically written to the next disk, which has the advantage of increasing the capacity of the disk.
Speed is the same as any one of the disks, and if any of these disks fail, the entire system will be compromised, reliably
Sex is the 1/n of a single hard drive.
(2), Another way of RAID 0 (commonly referred to as RAID 0 refers to this)
is to create a stripe set with a reasonable stripe size of n hard drives, preferably with a dedicated disk controller for each drive, which increases n times the speed of reading and writing data to n disks while the computer is reading and writing data. Improve the performance of the system.

2, RAID 1 (also known as mirror or mirroring--mirror)
RAID 1 is called disk mirroring: The data of one disk is mirrored on another disk, and the reliability and repairable of the system can be guaranteed without compromising the performance, it has high data redundancy, but the disk utilization is 50%, so the cost is the highest, and it is used in the case of saving critical important data. RAID 1 is done by automatically copying the data that the user writes to the drive to a different hard disk.

RAID 1 has the following features :
(1), RAID 1 each disk has a corresponding mirror disk, at any time the data are synchronized mirroring, the system can be from a set of mirrors on any disk to read data.
(2), the disk can use space only half the total disk capacity, the system cost is high.
(3), as long as there is at least one disk in any pair of mirrors in the system can be used, and even in half the number of hard disk problems when the system can operate normally.
(4), a hard disk failure of the RAID system is no longer reliable, should promptly replace the damaged hard disk, or the remaining mirror disk also has problems, then the entire system will crash.
(5), after the replacement of the original data will take a long time to synchronize the image, the external access to the data will not be affected, but the performance of the entire system has declined.
(6), RAID 1 disk controller load is quite large, with multiple disk controllers can improve the security and availability of data.

How RAID 1 works:

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Figure 2

2: When reading the data, the system first reads the data from the RAID1 source disk, if the reading data is successful, the system does not take care of the backup disk data, if the reading of the source disk data fails, the system automatically read the data on the backup disk, will not cause the user's work task interruption. Of course, we should replace the damaged hard drive in time and re-establish the mirror with the backup data to avoid the irreparable loss of data in the event of damage to the backup disk.
Advantages and disadvantages of RAID 1
With a full backup of the stored data, RAID 1 provides the highest data security across all RAID levels. Similarly, with 100% backups of data, backup data accounts for half of total storage space, thus mirror (mirrored) disk space utilization is low and storage costs are high. Mirror does not improve storage performance, but because of its high data security, it is especially suitable for storing important data, such as server and database storage areas.

3, RAID 5 (can be understood as a compromise of RAID 0 and RAID 1, but not fully using the RAID 1 mirroring concept, but using "parity information" as the data recovery method, unlike the following RAID10. ）

Fault tolerance:	Yes	Redundancy Type:	Parity check
Hot Spare options:	Yes	Read performance:	High
Random Write performance:	Low	Continuous Write performance:	Low
Number of disks required:	Three or more
Available capacity:	(n-1)/n Total disk Capacity (n is the number of disks)
Typical applications:	Random data transmission requires high security, such as finance, database, storage and so on.

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Figure 3
RAID 5 is a storage solution that combines storage performance, data security, and storage costs. For example, RAID 5, which consists of four hard disks, is stored in data Mode 4: The AP is the parity information for A1,A2 and A3, and so on. As can be seen from the figure, RAID 5 does not back up the stored data, but instead stores the data and the corresponding parity information on each disk that makes up the RAID5, and the parity information and the corresponding data are stored on separate disks. When one of the RAID5 disk data is damaged, the remaining data and the corresponding parity information are used to recover the corrupted data.
RAID 5 can be understood as a compromise between RAID 0 and RAID 1. RAID 5 can provide data security for the system, but with a lower level of protection than mirror and higher disk space utilization than mirror. RAID 5 has a similar data read speed as RAID 0, with only one parity information, which is slower than writing to a single disk. And because multiple data corresponds to one parity message, RAID 5 has a higher disk space utilization than RAID 1 and a relatively low storage cost.

4.Raid 10 is a raid 0 with Raid1 parity implements stripe set mirroring, so it inherits the RAID0 's fast and RAID1 security. We know that RAID 1 is a redundant backup array here, while RAID 0 is responsible for reading and writing the data array. In fact, Figure 4 is only a raid 10 way, more cases are separated from the main channel two, do striping operation, that is, the data segmentation

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Figure 4

RAID10 is also known as a mirror array strip. Like RAID0, data is pumped across the disk; like RAID1, each disk has a mirror disk, so another way to say RAID 10 is raid 0+1. The RAID10 provides 100% data redundancy to support larger volume sizes, but the price is also relatively high. RAID10 provides the best performance for most applications that require only redundancy, regardless of price. With RAID10, you get better reliability, because even if two physical drives fail (one in each array), the data can still be protected. RAID10 requires 4 + 2*n disk drives (N >=0), and can only use half (or smaller, if the disk size is different) disk usage, such as 4 250G hard disk using RAID10 array, the actual capacity is 500G.

RAID Summary:

Type	Read/write performance	Security	Disk Utilization	Cost	Application aspects
RAID0	Best (improved by parallelism)	Worst of all (no security guaranteed)	Highest (100%)	Minimum	Individual users
RAID1	Read and single disk no difference, write to write to both sides	Highest (100% backup for data)	Poor (50%)	Highest	It is suitable for storing important data such as server and database storage areas.
raid5	read: RAID 5=raid 0 (similar data reading speed) &NBSP; write: RAID 5< write to a single disk (more than one parity message is written)	raid 5<raid 1<= "" td= "" style= "Word-wrap:break-word;"	raid 5>raid 1	RAID 5< Raid 1<= "" td= "" style= "Word-wrap:break-word;"
RAID10	READ: RAID10=RAID0 Written by: Raid10=raid1	Raid10=raid1	RAID10=RAID1 (50%)	Raid10=raid1	The advantages of RAID0,RAID1 are set, but the disk utilization is as much as 50% because of the use of mirroring instead of "parity information" like RAID5 in space.

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RAID0, 1, 5, 10 detailed