Shulou(Shulou.com)06/01 Report--

RAID is the abbreviation of Redundant Array of Independent Disks in English and redundant array of independent disks in Chinese. RAID is a redundant array of hard disks. Although RAID contains multiple hard drives, it appears as a separate large storage device under the operating system. There are three main benefits of using RAID technology for storage systems:

1. Provides disk spanning by organizing multiple disks together as a single logical volume

two。 Improve disk access speed by dividing data into multiple data blocks (Block) to write / read multiple disks in parallel

3. Provide fault tolerance through mirroring or verification operations.

Characteristics of RAID

RAID-0:

RAID 0: merges multiple disks into one large disk without redundancy. It is the fastest in parallel. RAID 0 is also called band set. It is a juxtaposition of multiple disks to form a large hard disk. When storing the data, it segments the data according to the number of disks, and then writes the data to these disks at the same time.

So, of all the levels, RAID 0 is the fastest. However, RAID 0 has no redundancy function, and if a disk is (physically) damaged, all the data cannot be used.

RAID-1:

RAID1 divides the hard disks in the disk array into the same two groups and mirrors each other. When any disk medium fails, it can use the data on the mirror to recover, so as to improve the fault tolerance of the system. The operation of the data still adopts the parallel transmission mode after being divided into blocks. All RAID 1 not only improves the speed of reading and writing, but also enhances the reliability of the system. But its disadvantage is that the utilization of the hard disk is low and the redundancy is 50%.

RAID-2

..

RAID-5:

RAID 5: writes data to disks in the array, and parity data is stored on individual disks in the array, allowing individual disk errors. RAID 5 also uses the check bits of the data to ensure the security of the data, but it does not store the check bits of the data on a separate hard disk, but stores the check bits of the data segments on each hard disk interactively. In this way, if any hard disk is damaged, the damaged data can be reconstructed according to the check bits on other hard drives. The utilization rate of the hard disk is nMel 1.

RAID-6

Improvement in reading and writing performance

Available space: (Nmur2) * min (S1, S2,...)

Fault tolerance: 2 disks

Minimum number of disks: 4,4 +

RAID10

Improvement in reading and writing performance

Available space: N*min (S1, S2,...) / 2

Fault tolerance: each group of images can only be broken by one piece at most.

Minimum number of disks: 4,4 +

RAID01

Common levels: RAID-0, RAID-1, RAID-5, RAID-10, RAID-50, JBOD

Here we use centos6, and there are two ways to implement this.

Hardware implementation mode

Software implementation mode

Implementation of the software RAID on CentOS 6:

Combined with md (multi devices) in the kernel

Mdadm: a modeled tool

Syntax format of the command: mdadm [mode] [options]

Supported RAID levels: LINEAR, RAID0, RAID1, RAID4, RAID5, RAID6, RAID10

Mode:

Create:-C

Assembly:-A

Monitoring:-F

Management:-f,-r,-a

: / dev/md#

Any block of equipment

-C: create a pattern

-n #: use # block devices to create this RAID

-l #: indicates the level of RAID to be created

-a {yes | no}: automatically creates the device file for the target RAID device

-c CHUNK_SIZE: indicates the block size

-x #: indicates the number of free disks

For example: create a RAID5 of 10G free space

-D: displays the details of raid

Mdadm-D / dev/md#

Management mode:

-f: Mark the specified disk as damaged

-a: add disk

-r: remove the disk

Observe the status of md:

Cat / proc/mdstat

Stop the md device:

Mdadm-S / dev/md#

Watch's command:

Syntax use: watch-n # 'COMMAND'

Options are commonly used:-n #; refresh interval, time unit "seconds"

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