Raid independent Disk real Array

Source: Internet
Author: User

RAID technology mainly includes RAID 0 ~ Raid 50 and other specifications have different focuses. common specifications include:



  RAID 0: RAID 0 continuously splits data by bit or byte and reads/writes data on multiple disks in parallel. Therefore, RAID 0 has a high data transmission rate, but it does not have data redundancy, therefore, it cannot be regarded as a real raid structure. RAID 0 only improves performance and does not guarantee data reliability. However, failure of a disk affects all data. Therefore, RAID 0 cannot be used in scenarios with high data security requirements.



  Raid 1: Data redundancy is achieved through disk data images, which generate mutually backed up data on pairs of Independent Disks. When raw data is busy, data can be directly copied from the image, so RAID 1 can improve read performance. Raid 1 is the most costly disk array, but provides high data security and availability. When a disk fails, the system can automatically switch to the image disk to read and write data without restructuring the invalid data.



  RAID 0 + 1: Also known as the raid 10 standard, it is actually a product that combines RAID 0 and RAID 1 standards, when data is continuously divided by bit or byte and multiple disks are read/written in parallel, the disk image is redundant for each disk. Its advantage is that it has both the extraordinary speed of RAID 0 and the high data reliability of RAID 1, but the CPU usage is also higher, and the disk utilization is relatively low.


  Raid 2: Data is distributed in blocks on different hard disks. The block unit is bit or byte, and the average error correction code (Haiming Code) is used) "encoding technology to provide error detection and recovery. This encoding technology requires multiple disks to store inspection and recovery information, making raid 2 more complicated and therefore rarely used in commercial environments.


  RAID 3: It is very similar to raid 2. Data is distributed in blocks on different hard disks. The difference is that raid 3 uses simple parity and stores the parity information on a single disk. If a disk is invalid, the parity disk and other data disks can be duplicated.


New data is generated. If the parity disk fails, data usage is not affected. RAID 3 provides a good transfer rate for a large amount of continuous data, but for random data, the parity disk will become the bottleneck of write operations.


  Raid 4: Raid 4 also blocks data and distributes the data on different disks. However, the disk unit is block or record. Raid 4 uses a disk as the parity disk. Each write operation requires access to the parity disk. In this case, the parity disk becomes the bottleneck for write operations. Therefore, raid 4 is rarely used in commercial environments.



  RAID 5: RAID 5 does not separately specify a parity disk, but cross-access data and parity information on all disks. On RAID 5, read/write pointers can be performed on the array devices at the same time, providing higher data traffic. RAID 5 is more suitable for small data blocks and random read/write data. The main difference between RAID 3 and RAID 5 is that each data transmission of RAID 3 involves all array disks. For RAID 5, most data transmission only operates on one disk and can be performed in parallel. There is a "Write loss" in RAID 5, that is, each write operation will generate four actual read/write operations, two of which read the old data and parity information, write new data and parity information twice.


  Raid 6: Compared with RAID 5, raid 6 adds the second independent parity information block. Two independent parity systems use different algorithms, and the data reliability is very high. Even if the two disks are invalid at the same time, the data usage will not be affected. However, raid 6 needs to allocate more disk space to the parity check information, which has a greater "Write loss" compared with RAID 5. Therefore, the "Write Performance" is very poor. Poor performance and complex implementation methods make raid 6 rarely applied in practice.


  Raid 7: This is a new raid standard. It comes with an intelligent real-time operating system and a software tool for storage management. It can run completely independently of the host and does not occupy host CPU resources. Raid 7 can be viewed as a storage computer, which is significantly different from other raid standards. In addition to the above standards (such as table 1), we can combine multiple raid specifications like RAID 0 + 1 to build the required raid array, such as RAID 5 + 3 (RAID 53) it is a widely used array. Generally, you can flexibly configure disk arrays to obtain a more suitable disk storage system.


  Raid 5E(RAID 5 enhencement): Raid 5E is an improvement based on RAID 5. Similar to RAID 5, data verification information is evenly distributed across hard disks. However, A portion of unused space is retained on each hard disk, which is not striped. A maximum of two physical hard disks can be faulty. It seems that raid 5E is similar to RAID 5's hot backup disk. In fact, raid 5E distributes data across all hard disks, and the performance is better than RAID 5's hot backup disk. When a hard disk fails, the data on the faulty hard disk is compressed to space not used on other hard disks, and the logical disk is RAID 5.


  Raid 5ee: Compared with raid 5E, the data distribution of RAID 5ee is more efficient. A part of the space of each hard disk is used as a hot spare disk for distribution, which is part of the array, when a physical hard disk in the array fails, the Data Reconstruction speed is faster.


  Raid 50: Raid50 is a combination of RAID5 and raid0. This configuration is used to strip data, including parity information, on each disk of the sub-disk group of RAID 5. Each RAID5 sub-disk group requires three hard disks. Raid50 is highly fault tolerant because it allows a disk in a group to fail without causing data loss. In addition, the reconstruction speed is greatly improved because the parity bit is located on the RAID5 sub-disk group. Advantage: higher fault tolerance capability and the potential for faster data reading speed. Note that disk failure affects throughput. The reconstruction information after the fault takes longer than the image configuration.

Disk Arrays can be implemented in two ways: "software arrays" and "Hardware arrays ".


  Software ArrayThe disk management function provided by the network operating system is used to configure multiple hard disks on the connected common scsicard into logical disks to form an array. The software array can provide data redundancy, but the performance of the disk subsystem may be reduced. Some software Arrays can reduce the performance by about 30%.


  Hardware ArrayIt is implemented using a dedicated disk array card. The hardware array provides functions such as online resizing, dynamic modification of the array level, automatic data recovery, drive roaming, and ultra-high speed buffering. It provides performance, data protection, reliability, availability, and manageability solutions. The special processing unit of the array card is used for operations. Its performance is much higher than that of conventional non-array hard disks, and it is safer and more stable.


Disk arrays are also divided into software raid and hardware raid. the soft array is achieved by the software program and the CPU of the computer. because the software program is not a complete system, it can only provide the most basic RAID fault tolerance function. other functions, such as hot backup hard disk settings and remote management, are not recommended. the hardware with independent operations provides the control and computing functions of the entire disk array. it does not rely on the CPU resources of the system.


Since the hard array is a complete system, all required functions can be implemented. therefore, the functions and performance of the hard array are better than those of the soft array. moreover, if you want to make the system a disk array, hard arrays are the only choice. therefore, we can see that the raid Level 5 disk arrays on the market are hard arrays. the soft array is only applicable to RAID 0 and RAID 1. we certainly do not use RAID 0 or raid 1 for the image tower we use for mirroring. As a high-performance storage system, it has been widely used. The level of raid has evolved from the concept of raid to six levels, including 0, 1, 2, 3, 4, and 5. However, the four most common levels are 0, 1, 3, and 5.

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