Detailed RAID Disk utilization

Detailed RAID Disk utilization

one. RAID definition
RAID (Redundant array of independent disks independent redundant disk array) technology is the University of California, Berkeley, 1987, originally to combine small low-cost disk to replace large expensive disk, At the same time you want to disable the disk will not make access to data loss and develop a level of data protection technology. RAID is a redundant array of inexpensive disks that appear as a stand-alone, large storage device under the operating system. RAID can give full play to the advantages of multiple hard drives, can improve the speed of the hard disk, increase capacity, provide fault-tolerant work can ensure data security, easy to manage the advantages of any one hard drive problems in the case can continue to work, will not be damaged by the impact of the hard drive.
second, several types of RAID mode of operation (only discuss the Raid0,raid1,raid5,raid10 four, which four typical)
1 , RAID0 (also known as stripe or striping--section)
That is, data stripping technology. RAID 0 enables multiple hard drives to be connected to a larger hard drive cluster, improving disk performance and throughput. RAID 0 has no redundancy or bug fixes and is low cost, requiring at least two disks, typically used only if the data security requirements are not high. Characteristics:

Fault tolerance:	No	Redundancy Type:	No
Hot Spare options:	No	Read performance:	High
Random Write performance:	High	Continuous Write performance:	High
Number of disks required:	Only 2 or 2*n (there should be more than two hard drives available)	Usable capacity:	Capacity of the total disk
Typical applications:	Quick read and write without fault, requires no high security, such as graphics workstation.

how RAID 0 works:

Figure 1 shows that the system's I/O data request to a three-disk logical hard disk (RADI 0 disk group) is converted to 3 operations, each of which corresponds to a physical hard disk. We can see clearly from the diagram that by setting up RAID 0, the original sequence of data requests are dispersed across all three hard drives.
In theory, the parallel operation of a three-disk drive increases the disk read-write speed by 3 times times in the same time. However, due to the bus bandwidth and other factors, the actual rate of ascension is certainly lower than the theoretical value, but, a large number of data parallel transmission and serial transmission comparison, the speed-raising effect is obviously beyond doubt.
of RAID 0Disadvantageis not providing data redundancy, so once the user data is corrupted, the corrupted data cannot be recovered.
RAID 0 is availablefeatures, so that it is particularly suitable for the high performance requirements, but not much care about the data security areas, such as graphics workstations. For individual users, RAID 0 is also a great choice for improving the performance of hard disk storage.
Computer technology has developed rapidly, but the transmission rate of hard disk has become a bottleneck of performance. What to do. The sophistication of the IDE RAID technology allows us to easily build our own ultra-high speed drives. In practical applications, the RAID 0 hard disk array can be much faster than the normal IDE 7200 to ATA 133 hard drives, and today, we can find a promise or Highpoint RAID chip on most high-end or player motherboards. Also discover the extra few IDE interfaces they provide. Yes, RAID is already in the offing, so are you willing to give up the performance boost that raid has brought us? The answer is, of course, negative.
　　 Practical IDE RAID
RAID can be implemented through software or hardware. Like Windows 2000, you can provide RAID capabilities for software, but this requires a very small CPU and reduces overall performance. The hardware implementation is generally implemented by the raid card, the high-end SCSI RAID card has its own dedicated cache and I/O processor, but for home users such a cost is obviously unbearable, after all, in order to achieve RAID to buy two or more of the HDD has been quite difficult. We also have a compromise approach to--ide RAID. Perhaps this is the easiest way for the average person to accept. Although IDE raid has a compromise in functionality and performance, the average user does not seem to care about the low price.
　　 Why should I use RAID 0
RAID 0 requires at least two hard drives to achieve, its capacity for the composition of the system's various hard disk capacity of the sum, the capacity of these pieces of the same, in the home IDE raid in the general Cascade two hard drives, must use the same model of the same capacity of the hard disk. When the RAID 0 mode writes data to the hard disk, it divides the data into two pieces, writes the data to both hard drives, and then, when it reads, it is the opposite, so that each hard disk will have to bear half of the data transfer task, and the result is the increase of the speed.Implementation mode:(1),The easiest way to RAID 0 (I don't think this is the way it was meant to be)
is to put the same hard drive in the same way as hardware in the form of a smart disk controller or by using the disk drivers in the operating system to cascade the software together. Form a separate logical drive, the capacity is X times the size of a single hard drive, written to each disk when the computer data is written, and when the space of a disk is exhausted, The data is automatically written to the next disk, and the advantage is that it can increase the capacity of the disk.
Speed is the same as any one of the disks, if any one of the disks fails, the entire system will be destroyed, reliability is the use of a single hard drive 1/n.
(2),Another way of RAID 0 (often referred to as RAID 0 means this)
is the use of N-block hard to choose a reasonable band size to create a stripe set, preferably for each hard disk is equipped with a dedicated disc controller, in the computer data reading and writing to the N-block disk reading and writing data, speed up n times. Improve the performance of the system.

2, RAID 1 (also known as mirror or mirroring--mirroring)
RAID 1 is known as disk mirroring: Mirroring a disk's data to another disk, without affecting the performance of the maximum guarantee system reliability and repairable, with high data redundancy, but disk utilization is 50%, so the highest cost, more used in the preservation of key important data occasions.       RAID 1 operates by automatically copying the data that the user writes to the hard disk to another hard drive. RAID 1 has the followingfeatures：
(1) Each disk of RAID 1 has a corresponding mirror disk, at any time the data is synchronized mirroring, and the system can read data from any disk in a set of mirrored disks.
(2), the disk can use 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, or even half a number of hard disk problems when the system can run correctly.
(4), the failure of the raid system is no longer reliable, should be timely replacement of the damaged hard disk, otherwise the remaining mirror disk also problems, then the entire system will collapse.
(5), replace the new disk after the original data will need a long time synchronous mirror, the external access to data will not be affected, only then 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.RAID 1 mode of work:

Figure 2 is shown in Figure 2: When reading the data, the system first reads the data from the source disk of the RAID1, if the data is successful, the system does not pipe the data on the backup disk, and if the source disk data fails, the system automatically reads the data on the backup disk without disrupting the user's work task. Of course, we should promptly replace the damaged hard disk and use the backup data to re-establish mirror, to avoid the backup disk in the event of damage, resulting in irreparable data loss.
Advantages and disadvantages of RAID 1
With a full backup of the stored data, RAID 1 provides the highest level of data security at all RAID levels. Similarly, backup data accounts for half of total storage space due to 100% of data backups, resulting in low disk space utilization and high storage costs for mirror (mirroring).  Mirror can 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 and other fields. 3, RAID 5 (understandable as a compromise between RAID 0 and RAID 1), but not fully using the RAID 1 mirroring concept, but using "parity information" as a way of recovering data, unlike the RAID10 below. )

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
Usable 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.

Figure 3
RAID 5 is a storage solution that combines storage performance, data security, and storage costs. Take RAID 5, which consists of four hard disks, as an example of how the data is stored as shown in Figure 4: In the figure, the AP is 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 a RAID5 disk data is corrupted, the corrupted data is recovered using the remaining data and the corresponding parity information.
RAID 5 can be understood as a compromise between RAID 0 and RAID 1. RAID 5 provides data security for the system, but is less secure than mirror and disk space utilization is higher than mirror. RAID 5 has the same data read speed as RAID 0, but one more parity information, which is slower to write data than to write to a single disk. At the same time, because multiple data correspond to parity information, RAID 5 has a higher disk space utilization ratio than RAID 1 and has a relatively low storage cost. 4, Raid 5 (understandable as a compromise between RAID 0 and RAID 1, but not fully using the RAID 1 mirroring concept, but using "parity information" as a way to recover data)        RAID10 is also known as a mirror array strip. Like RAID0, data is extracted across disks; like RAID1, each disk has a mirror disk, so another version of RAID 10 is a raid 0+1. RAID10 provides 100% data redundancy, supports larger volume sizes, but also has a relatively high price. RAID10 provides the best performance for most applications that only require 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 only half (or smaller, if the size of the disk) is used, such as 4 250G hard disks using RAID10 array, and the actual capacity is 500G.   Personal Summary:  

Type	Read and write performance	Security	Disk Utilization	Cost	Application aspects
RAID0	Best (increased by parallelism)	Worst (no safety guarantee at all)	Highest (100%)	Minimum	Individual users
RAID1	Read and single disk no different, write to write on both sides	Highest (100% backup of data available)	Difference (50%)	Highest	Suitable for storing important data, such as server and database storage.
RAID5	READ: Raid 5=raid 0 (similar data read speed) write: Raid 5< writes to a single disk (more than one parity information is written)	RAID 5<raid 1	RAID 5>raid 1	RAID 5<raid 1	is a storage solution that combines storage performance, data security, and storage costs.
RAID10	READ: Raid10=raid0 write: Raid10=raid1	RAID10 =RAID1	RAID10 =raid1 (50%)	RAID10 =RAID1	The benefits of RAID0,RAID1 are set, but space is 50% as a result of using mirroring rather than "parity information" like RAID5

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