RAID_Redundant-Array-of-Independent-Disks

------------------------ RAID -----------------------------------------


---------- Introduction:

The disk array is short for RAID (Redundant Arrays of Inexpensive [Independent] Disks, RAID), meaning "cheap and Redundant disk Arrays. The principle is to use arrays as disk groups and use them in combination with the Design of Distributed Data arrangement to improve data security. The disk array mainly targets hard disks. in terms of capacity and speed, it cannot keep up with the development of CPU and memory, and proposes improvement methods. A disk array is a large disk, which is made up of many Inexpensive Disks with low capacity, high stability, and slow speed, improve the efficiency of the entire disk system by using the bonus Effect of data provided by individual disks. At the same time, this technology is used to cut data into many segments and store them on various hard disks.


The disk array has three styles,
First, external disk array cabinets,
Second, internal disk array cards,
Third, use software for simulation.

Note: 1. External disk array cabinets are most often used on large servers with Hot Swap, but these products are expensive.
2. The internal disk array card is suitable for technical personnel to use because it is cheap but requires high installation technology.
3. The software simulation method is not suitable for servers with big data traffic because it will drag down the machine speed.


The stability and performance of the IDE interface hard disk have been greatly improved. In addition to cost considerations, it is the best way to use the IDE interface hard disk as a disk array solution.



-------- Related concepts:

1. What is a Disk Array )?
A Disk Array is a 'one hard Disk controller' that controls the connection between multiple hard disks. This allows you to 'read/Write synchronization' for multiple hard disks to reduce errors, technologies that increase efficiency and reliability.
　    
2. What is RAID?
RAID, short for Redundant Array of Inexpensive Disk, is a cheap Redundant Disk Array, the objective is to reduce errors and improve the performance and reliability of the storage system. Common levels include 1, 3, and 5.
　
3. What is RAID Level 0?
RAID Level 0: it is the implementation of Data Striping ('data partition') technology. It makes all hard disks into a disk array,
You can 'read and write' multiple hard disks at the same time,
But [[not capable of backup and fault tolerance], it is cheap,
The hard disk uses [[optimal efficiency], but the reliability is the worst.

Taking a RAID Level 0 disk array composed of two hard disks as an example,
It writes 1st and 2 digits of data to the first hard disk, and the third and fourth digits to the second hard disk ...... And so on,
Therefore, it is called "data segmentation". Because the write operations of data on each disk are done at the same time, the storage speed can be several times faster than that of a single hard disk.
    
However, in this case, if a hard disk on the disk array breaks down, the data is stored separately on different hard disks,
If a broken tape breaks down the integrity of the data, all the data cannot be recovered without the backup tape of the entire disk array.
Therefore, despite its high efficiency, few are risking data loss to use this technology.
　

4. What is RAID Level 1?
RAID Level 1 uses the Disk Mirror (Disk ror ing) technology to replicate the content of one hard Disk to another. Therefore, it is capable of backup and fault tolerance, in this way, the efficiency is not high, but the reliability is high.
　　    
5. What is RAID Level 3?
RAID Level 3 uses Byte-interleaving (Data staggered storage) technology to operate the hard disk simultaneously on/* SCSI controller, the data used for 'parity check' is stored in a specific hard disk. It has the fault tolerance capability. The 'efficiency of the hard disk is to reduce the usage by a few ', and its reliability is better.
　　    
6. What is RAID Level 5?
RAID Level 5 uses the Disk Striping technology, which is different from Level 3 in that it stores the parity data in each hard Disk ', each hard disk operates in parallel under the control of the/* SCSI control card */and has fault tolerance capabilities. Like Level 3, its 'usage efficiency is also reduced when it is installed. '
　　
7. What is a hot swapping hard drive?
Hot-Swappable Disk is an English name Hot-Swappable Disk. In a Disk array, if a hard Disk that supports Hot-Swappable technology is used, 'servers do not need to shut down when one hard Disk breaks down ', remove the broken hard disk and replace it with a new one. When a general commercial disk array breaks down the hard disk, it will automatically prompt the Administrator to change the hard disk.
    



-------- Software simulation RAID5 (RHEL5.5)

* ****** 1. Partition:

A. [root @ localhost md] # fdisk/dev/sda

Command (m for help): n
First sector (23277568-27262975, default 23277568 ):
Using default value 23277568
Last sector, + sectors or + size {K, M, G} (23277568-23279615, default 23279615): + 10 K

Command (m for help): n
First sector (25378816-27262975, default 25378816 ):
Using default value 25378816
Last sector, + sectors or + size {K, M, G} (25378816-27262975, default 27262975): + 10 K

Command (m for help): n
First sector (25380884-27262975, default 25380884 ):
Using default value 25380884
Last sector, + sectors or + size {K, M, G} (25380884-27262975, default 27262975): + 10 K

Command (m for help): t
Partition number (1-8): 6
Hex code (type L to list codes): fd
Changed system type of partition 6 to fd (Linux raid autodetect)

Command (m for help): t
Partition number (1-8): 7
Hex code (type L to list codes): fd
Changed system type of partition 7 to fd (Linux raid autodetect)

Command (m for help): t
Partition number (1-8): 8
Hex code (type L to list codes): fd
Changed system type of partition 8 to fd (Linux raid autodetect)

Command (m for help): w
The partition table has been altered!


B. Reload the Partition Table

[Root @ localhost dev] # partprobe


* ****** 2. Combination (create Disk Array)

Mdadm-C/dev/md1-l 5-n 3/dev/hda {6, 7, 8}



* ***** 3. Format

Mkfs. ext3/dev/md1


* ***** 4. Mount

A. mount/dev/md1/mnt/abc

// After mounting, you can go to the abc Directory: lost + found (used to store sub-object files without parent directory)

B. vim/etc/fstab

Mount disk array Mount directory file system mount mode (read | write) backup (1 slave; 0 slave) scan option (root directory first scan: 1, other level> 1, or 0: No scan)
/Dev/md1/mnt/ABC ext3 default (default) 0 1

Mount-A // re-mount all items in fstab


##### Other viewing commands


1. dumpe2fs-H/dev/md1 // view the ext2/ext3 file system information of md1

2. mdadm -- detail/dev/md1 // view md1 details, including organization information

3. CAT/proc/mdstat // view raid combo disk Information