Brief description of RAID type and implementation of soft raid on level Linux system

Early due to raid is often used to combine some inexpensive SATA interface hard disk devices to complete redundancy.

So the early full name is: redundantarray of independent Disks (independent redundant disk array).

The primary function of RAID is to combine multiple hard disks on the motherboard in a specific way, organized into a logical whole with specific characteristics, and then output to the operating system or application. Depending on the combination, you can make the logic whole redundant or speed up the characteristics of the data storage. This logical whole, with certain characteristics, is called a RAID array.

RAID is divided into software RAID and hardware RAID depending on how it is implemented. Here's a look at software RAID and hardware RAID:

Software RAID: Software RAID is built on the basis of the operating system, the first need to install the operating system on disk, then the user then use the function of the operating system kernel combined with the user application space program on the system recognized block device to create raid. Any block device on a Linux system can be built into raid with the MDADM command combined with the MD module in the kernel. RAID created in this way also has the feature of redundancy or accelerated data storage, provided that the block device being created is not on the same hard disk. Of course, soft raid consumes CPU computing power when data chunked storage is implemented, so most enterprises do not use this method to do RAID array.

Hardware RAID: Hardware RAID is established before the operating system starts, configuration raid is generally done in the BIOS and RAID array card interface. A RAID array card is actually a RAID controller that can be connected to multiple disks. Some of the array cards are integrated on the motherboard, and some are mounted on the motherboard slots. RAID array cards are generally with CPU-like processing chips, high-end point of the array card with memory and battery. The hard drive device that is connected to the array card can be configured for RAID before the system boots, which is the equivalent of a hard disk for the operating system to use after the system is booted. Of course, when the operating system is installed, the operating system needs to install the drive of the RAID array, or the operating system will not recognize the RAID array. RAID arrays created in this way are created with a RAID array card, and the raid card has a self-contained processor, so this method does not need to consume CPU computing power when performing data processing work. Can greatly improve the performance of RAID. That's why most businesses like to do raid arrays in this way.

After the soft raid and hard raid, let me say the basic RAID level. The following are common:

Levels (Level)	Raid0
Characteristics	Data is stored evenly on every drive
Minimum number of disks	2
Disk requirements	The capacity of each disk must be the same size, preferably the same manufacturer of the same model
Redundancy capability	No
Read/write performance	Improve
Free space	Number of disks * single-block disk capacity

Levels (Level)	Raid1
Characteristics	Each piece of data is stored in one copy on each drive.
Minimum number of disks	2
Disk requirements	The capacity of each disk must be the same size, preferably the same manufacturer of the same model
Redundancy capability	Strong
Read/write performance	Write performance degradation, read performance enhancement
Free space	Single-Block disk capacity

Levels (Level)	Raid4
Characteristics	The data is stored evenly on the (n-1) hard drive, the checksum is generated when stored, and the checksum is stored on the hard disk specified in the RAID4, which does not store the file data
Minimum number of disks	3
Disk requirements	The capacity of each disk must be the same size, preferably the same manufacturer of the same model
Redundancy capability	Strengthen
Read/write performance	Improve
Free space	(Number of disks-1) * Single-block disk capacity

Levels (Level)	Raid5
Characteristics	The data is stored evenly on the (n-1) hard drive, and a checksum is generated when stored, and the checksum is stored on the disk of the RAID5 array in turn.
Minimum number of disks	2
Disk requirements	The capacity of each disk must be the same size, preferably the same manufacturer of the same model
Redundancy capability	Strengthen
Read/write performance	Improve
Free space	(Number of disks-1) * Single-block disk capacity

In addition to the above basic raid, RAID10 and RAID50 are also raid combinations. Where RAID10 is the most common of these combinations is to do RAID1 first, and then RAID1 in combination into RAID0, which can be improved. Let me give you an example:

In the red box in the blue box inside the two disk to do is RAID1, and then three raid1 into a raid0, then the combination is called RAID10.

Brief description of RAID type and implementation of soft raid on level Linux system