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  Examples of RAID levels and achieve Operational Details
  Add Date : 2018-11-21      
  One, RAID Brief History

1.RAID Origin

Berkeley: Berkeley proposed: A case for Redundent Arrays of Inexpensive Disks as RAID (Redundant Array of Inexpensive)

Today: Redundant Arrays of Independent Disks Redundant Array of Independent

2. The advantages and expressions

1) through parallel disk read and write, the ability to improve IO:

2) by disk redundancy (fault tolerance) mechanisms to achieve greater durability:

3. Level: multiple disks organizations work together differently


4. implementation

(1) software simulation to achieve: Software RAID, combine kernel md (multi devices) Tools

Production environment generally are not in use

(2) hardware: hardware-level RAID configurations across multiple disks to achieve in the bios

External disk arrays: providing adaptation capacities through an expansion card

Inscribed formula RAID: motherboard integrated RAID controller

1) can be extended through the SAS interface, serial port adapter interface attached storage to logical unit number LUN performance

Narrowband: 8 interfaces, 7target

Broadband: 16 interfaces, 15 target

2) RAID controller requires drivers to use the system, the BIOS can be set to connect to the RAID via adapter

3) RAID controller itself a CPU, a memory can also be accelerated, another way to set the power off when the emergency is written

Two, RAID level and mode of operation

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

1.RAID-0: 0, striped volume, strip;

Performance: read, write performance; no fault tolerance

Space used: N * min (S1, S2, ...),

Requires a minimum number of disk: at least two

Bands: the smallest capacity disk will block the production of disk-based strip

2.RAID-1: 1, mirrored, mirror;

Performance: read performance, write performance declined slightly; with redundant capability

Space used: 1 * min (S1, S2, ...), each storing the same content

Space utilization: 1/2

Requires a minimum number of hard drives: at least two

3.RAID-4: a single disk as a central parity disk

Independent access mode, the strip from the RAID3 of small data blocks to larger blocks of data

Check more quickly, but the write speed is poor, more complex controller design

XOR by one of the drives, centralized storage checksum

Allows a hard disk is damaged, but because the focus check cause performance bottlenecks

4.RAID-5: cyclic check storage mechanism

Performance: read and write performance, fault tolerance: a disk

Use of space: (N-1) * min (S1, S2, ...) short-board effect

Space utilization: (n-1) / n

Minimum Disks: at least three, may downgrade

5.RAID-6: cyclic check storage mechanism, a hard disk specialize parity disk, check code stored twice

Performance: read, write performance; fault tolerance: 2 Disk

Space used: (N-2) * min (S1, S2, ...)

Minimum Number of disks: at least four

6.RAID-7: Business

The new RAID standard, a separate "computer storage", with its own real-time operating systems and intelligent storage management software tool is used, you can run completely independent of the host, do not take up host CPU resources

7.RAID-10: do first mirror, then a strip

Performance: reading, writing and promotion, there is redundancy

Space utilization: 1/2

Minimum Number of disks: At least 4

8.RAID-01: do first bands to do the mirror

Performance: reading, writing and promotion, there is redundancy

Space utilization: 1/2

Minimum Number of disks: At least 4


Performance: reading and writing promotion; redundant capability

Space utilization: (n-2) / n

Minimum Number of disks: At least 6

10.JBOD: Just a Bunch Of Disks multiple disk space will incorporate a large continuous space usage

Performance: no lift; no redundancy

Use of space: the size of the disk and the sum (S1, S2, ...)

Space utilization: 100%

Minimum Number of disks: At least 2

Three, RAID kernel implements observations related commands

Achieve CentOS 6 on software RAID

1.md (multi devices) tools, mdadm: modular tools

The syntax of the command: mdadm [mode] [options]

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

Mode: Create: -C; assembly: -A; Monitoring: -F; management: -f, -r, -a

: / dev / md #

: any block device

(1) -C: Create Mode

-n #: # use a block device to create this RAID;

-l #: RAID level specified to be created;

-a {yes | no}: Target RAID device to automatically create a device file;

-c CHUNK_SIZE: specified block size; the default 512k

-x #: specify the number of idle disks;

(2) management:

-f: Specifies the disk marked as damaged;

-a: Adding a Disk

-r: Remove Disk

(3) -D: show detailed information of the raid; mdadm -D / dev / md #

(4) observation md state: cat / proc / mdstat

(5) Stop md devices: mdadm -S / dev / md #

2.watch: dynamic observation command during operation

Format: watch -n # 'COMMAND'

-n #: refresh interval in seconds;
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