What is a disk array and why do you need one?

Many people know RAID 0, but do not understand disk array, their own life has never used it, how it works, whether it is really that powerful, today to take you to understand the disk array, first of all, to make clear that disk array only applies to multiple hard disks, a single hard disk cannot form an array, and when you have multiple hard disks, Under normal circumstances, each disk is independent of each other, non-interference, disk utilization can not be fully played, often only one hard disk in the continuous work, "a disk is difficult, eight disks to watch" the scene frequently appears in each computer, the above situation is referred to as JBOD mode, that is, each disk is independent of each other. When multiple hard disks are formed into a disk array, the working mode will change. We can understand that an array is to make full use of the disks and maximize the performance of each hard disk, namely RAID. When multiple hard disks are run in disk array mode, the system recognizes only RAID disks, but does not display physical disks. However, the function and usage method are the same, and they are all used to store data.

At present, there are 7 levels of RAID modes that are widely recognized, which are 0-7 respectively. Different RAID modes have different working modes and different test priorities. It is better to choose according to your own situation.

RAID 0

RAID 0 works in the same mode as dual-channel RAM. The read/write speed is doubled. However, due to the mechanical structure, the random read/write speed is limited.

RAID 1

RAID 1, also known as mirroring mode, is the most secure RAID mode. It works by using one hard disk as the primary disk and the other as the backup disk for local real-time backup. When data is written to drive A, drive B also writes a copy of data in real time.

RAID 2

RAID D2 uses Haiming code verification to enhance data error correction capability on the basis of RAID 0. Important points: Error correction is not equal to disaster recovery. Because the mode is a little complex, we will not explore it further.

RAID 3

RAID 3 requires at least three hard disks. Two of the hard disks store routine data and the other one stores the data recovery codes of the first two hard disks. If one of the other two hard disks is damaged, the parity codes can be used to restore data. Compared with RAID 0, it has certain disaster recovery capability and the speed is similar to that of RAID 0. It can be interpreted that an extra recovery disk is set up on the basis of RAID 0.

RAID 4

Similar to RAID 3, RAID 4 is an enhanced version of RAID 0. The difference is that RAID 3 splits data and calculates parity codes for small files. RAID 4 packages files and only calculates parity codes for a large file.

RAID 5

RAID 5 is similar to RAID 3 and RAID 4 when the number of hard disks is small. As the number of hard disks increases, recovery disks limit the performance of the entire array. RAID 5 is an upgrade based on this. RAID 5 provides similar performance to RAID 0, solves the bottleneck of RAID 4 in a clever way, and has good disaster recovery capability. Therefore, RAID 5 has become the most widely used array mode.

RAID 6

RAID 6 adds a Dr Hard disk on the basis of RAID 5, focusing on the non - disk that may fail both hard disks.

RAID 7

RAID 7 is significantly different from the RAID levels we've seen. RAID 7 is an independent storage computer with an operating system and management tools. It can run independently.

To sum up

RAID 0: High speed, no disaster recovery capability, and high utilization RAID 1: normal speed, strong disaster recovery capability, and low utilization

RAID 2: provides high speed, error correction capability, and no disaster recovery capability

RAID 3/4: Add a Dr Disk on top of RAID 0. The Dr Disk controls the entire array

RAID 5: Delete fixed Dr Disks and store data and recovery codes on different disks. RAID 6: Two Dr Disks

RAID 7: Different from the preceding modes, RAID 7 can exist independently

RAID 10 is actually a RAID 0 mode composed of multiple hard disks, and then a RAID 1 array composed of multiple RAID 0 disks.