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Basic Knowledge Points about Raid.

I. The Basic Principles of Raid

RAID (Redundant Array of Independent Disks) is a redundant array of independent disks, usually referred to as disk array. Simply put, RAID is a disk subsystem composed of several independent high-performance disk drives, thus providing higher storage performance and data redundancy technology than a single disk. In the whole system of server, RAID is regarded as a storage space consisting of two or more disks, which can improve the I/O performance of storage system by reading and writing data concurrently on multiple disks. If you want to raid recovery, you need the data recovery software.

Common RAID Types

1) RAID 0

By dispersing continuous data to multiple disks for access, the system can execute data requests in parallel with multiple disks, and each disk executes its own part of the data requests. To make RAID 0, a server needs at least two hard disks, which can read and write twice as fast as a hard disk. If there are N hard disks, then the speed of reading and writing is N times faster than that of a hard disk. Although the speed of reading and writing can be improved, because there is no data backup function, the security will be much lower.

Fig. 1 RAID 0

2) RAID 1

Data redundancy is achieved through disk data mirroring, which generates backup data on paired independent disks. When the original data is busy, the data can be read directly from the mirror copy. Similarly, RAID1 requires at least two hard disks. When reading data alone, one is read and the other is used as backup data. Its data security will be higher, but the utilization of disk space is relatively low.

Fig. 2 RAID 1

3) RAID 5

RAID 5 stores data and corresponding parity information on the disks that make up RAID 5, and parity information and corresponding data are stored on different disks respectively. When one of the disks (up to one) is damaged, the damaged data is recovered using the remaining data and the corresponding parity information. RAID 5 has the same data reading speed as RAID 0, and the utilization of disk space is higher than RAID 1, and the storage cost is relatively low. It is a solution that is used more at present. If users choose RAID 5, they need at least three hard disks.

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