Soft RAID-mdadm tossing note

Soft RAID-mdadm tossing note

RAID-a disk array. In short, it is used to improve the utilization and speed of hard disks.
RAID type (theory ):
RAID 0: read/write performance (at least two hard disks)-hard disk usage is the sum of all hard disks and performance is the sum of all hard disks.
RAID 1: read/write performance, redundancy (at least two hard disks) --- space utilization: the smallest of all disks (n/2); read performance is close to RAID 0, the write performance is weaker than raid 0; The Write Performance is redundant.
RAID 5: read/write performance, redundancy (at least 3 hard disks) --- space utilization: 1-1/n. the read performance is close to RAID0, And the write performance is weaker than RAID0. redundancy: Damage to a hard disk is acceptable;
RAID 6: read/write performance, redundancy (at least 4 hard disks) --- space utilization: 1-2/n. compared with RAID 5, the read/write performance is weaker than RAID 5. redundancy: two hard disks may be damaged;
Mdadm common parameters

(Highlighted ):

-F: fail. Set a disk to a faulty state.
-L: LEVEL. Set the disk array LEVEL.
-R: Remove faulty device
-A: Add new devices to the disk array.
-S: stops a disk array.
-V: -- verbose: display details
-D, -- detail: Print details of one or more md Devices
-X: -- spare-devices: Specifies a backup disk, that is, the number of redundant devices of the initial array, that is, the number of spare devices;
-N: Number of disks
-A: -- assemble: adds A previously defined array.
-B: -- build: Create an array without Super blocks (Build a legacy array without superblocks .)
-C: -- create: create a new array
-F: -- follow, -- monitor: Select monitoring mode
-G: -- grow: changes the size or form of the activated array.
-I: -- incremental: Add a separate device to the appropriate array and possibly start the array.
-- Auto-detect: Requests the kernel to start any automatically detected Array
-H: -- help: help information. This option is displayed after the preceding options are used.
-- Help-options: displays more detailed help information.
-V: -- version: prints the mdadm version.
-B: -- brief: less details. Used for -- detail and -- examine options
-Q: -- query: view a device and determine whether it is a md device or a part of a md array.
-E: -- examine: print the content of the md superblock on the device.
-C: -- config =: Specifies the configuration file. The default value is/etc/mdadm. conf.
-S: -- scan: scan the configuration file or/proc/mdstat to search for lost information. Configuration file/etc/mdadm. conf

Use mdadm to create RAID (the level is only a number, and other parameters are basically the same ..)
CRATERAID 0:
[Plain] mdadm-Cv/dev/md0-l 0-n 2/dev/sdb/dev/sdc // single line comment: /dev/sdb/dev/sdc can be replaced by/dev/sd [B, c]
Format mounting:



Save the configuration to prevent array loss after restart:


CRATERAID1: [html] mdadm-Cv/dev/md0-l 1-n 2/dev/sdb/dev/sdc
CRATERAID5:

In order to continue creating the demo RAID5, let's talk about some stuff in advance and clear the RAID data...

If there is a mount before cleaning, you must detach it. Then stop the RAID array. Otherwise, an error will be reported.
The following parameters are used:-S, -- zero-superblock.
[Plain] mdadm-Cv/dev/md0-l 1-n 5/dev/sd [B, c, d]-x 1/dev/sde

CRATERAID6: [plain] mdadm-Cv/dev/md0-l 1-n 6/dev/sd [B, c, d, e]-x 1/dev/sdf
Advanced: Set faulty devices, remove devices, and replace disk devices

Set the faulty device: [plain] mdadm/dev/md5-f/dev/sdd


View status:


Remove faulty device: [plain] mdadm/dev/md5-r/dev/sdd


Check the details and you will find that the hard disk/dev/sdd is missing, but it is running well ....

Add a disk device: [plain] mdadm/dev/md5-a/dev/sdd


Set the RAID array to boot [plain] vim/etc/fstab
Insert in the last row
/Dev/md5/mnt ext4 default 0 0
 
Then return to the command mode: x or: wq save and exit
Note: to add a RAID entry to fstab, the corresponding format must be formatted and mounted ....