Raid overview and differences

Raid was proposed by several people such as 1988. Since then, the disk array technology has developed rapidly and gradually matured. Raid and high performance (performance) are organized together by multiple disks as a logical volume to provide the disk crossing Function
Oslash; read multiple disks to speed up disk access. raid0 is distributed across multiple physical disks and can read/system data in parallel with high performance and the lowest cost. Because there is no fault tolerance function, raid0 is suitable for low-cost, low-reliability desktop systems, where high-speed data throughput is more important than reliability.
Raid1 uses image fault tolerance to improve reliability. That is, each working disk has an image disk. Each time data is written, it must be written to the image disk at the same time. Data is read only from the work disk. If a work disk fails, it is immediately transferred to the image disk. The data is read from the image disk, and the system then restores the correct data on the Work disk. Therefore, data in this way can be reconstructed, but the work disk and the image disk must have a one-to-one relationship. This disk array is highly reliable, but its effective capacity is reduced to less than half of the total capacity. Therefore, raid1 is often used in applications that require extremely strict error rates, such as finance and other fields. Only one hard disk is allowed to fail.
Raid3 comes with a dedicated validation disk sharding technology. Data is distributed across multiple disks to speed up reading and writing, and a dedicated disk is used to store verification information. When a member disk fails, the controller can recover lost data RAID 5 from the verification disk, but the verification data is not stored on a dedicated verification disk, but distributed on multiple disks. When one disk fails, the controller can recover/disk from another existing disk, capacity is (the N-1 allows concurrent write operations in the same group. Therefore, RAID5 is suitable for large data volume operations and various transaction processing. It is a fast, high-capacity, and fault-tolerant disk array. Only one hard disk is allowed to fail.
Raid3 and RAID5 performance raid3 no matter which disk is written to, the disk needs to be written to the verification disk, so the verification disk will become the bottleneck for writing big data, so it is only suitable for writing less data, querying multiple applications (Web) RAID5 puts the verification data on different disks, apportioned the read/write pressure, thus avoiding raid3 performance problems.