mdadm introduction

Management software raid tool: mdadm

mdadm is a command used to create and manage software RAID under linux. It is a modal command

Parameters of the mdadm command

-C build a new array
-A activate disk array
-a add device to array
-D print array device details
-s scan configuration file or / proc/mdstat to get array missing information
-v display details
-r remove device
-f set the equipment status as failure
-l set the level of the disk array
-n specifies the members of the disk array (number of partitions / disks)
-x specifies the number of spares in the array

Actual combat raid 0

Two new hard disks

[root@centos7-xinsz08 ~]# ll /dev/sd*
BRW RW ---- 1 root disk 8, 2 / 27 14:49 /dev/sda
 BRW RW ---- 1 root disk 8, 1 February 27 14:49 /dev/sda1
 BRW RW ---- 1 root disk 8, February 27 14:49 /dev/sda2
 BRW RW ---- 1 root disk 8, February 27, 2016 14:49 / dev / SDB
 BRW RW ---- 1 root disk 8, 32 February 27 14:49 /dev/sdc
[root@centos7-xinsz08 ~]# fdisk /dev/sdc
 Welcome to fdisk (util Linux 2.23.2).

Changes stay in memory until you decide to write them to disk.
Think twice before using the write command.

Device does not contain a recognized partition table
 Use disk identifier 0xb7cb3eac to create a new DOS disk label.

Command (enter m for help): n
Partition type:
   p   primary (0 primary, 0 extended, 4 free)
   e   extended
Select (default p): p
 Partition number (1-4, default 1):
Start sector (2048-41943039, default 2048):
The default value 2048 will be used
 Last sector, + sector or +size{K,M,G} (2048-41943039, default is 41943039): + 5G
 Partition 1 is set to Linux type and size is set to 5 GiB

Command (enter m for help): n
Partition type:
   p   primary (1 primary, 0 extended, 3 free)
   e   extended
Select (default p): p
 Partition number (2-4, default 2):
Starting sector (10487808-41943039, default is 10487808):
The default value 10487808 will be used
 Last sector, + sector or +size{K,M,G} (10487808-41943039, default is 41943039): + 5G
 Partition 2 is set to Linux type and size is set to 5 GiB

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

Calling ioctl() to re-read partition table.
Synchronizing disks.
[root@centos7-xinsz08 ~]# ll /dev/sd*
BRW RW ---- 1 root disk 8, 2 / 27 14:49 /dev/sda
 BRW RW ---- 1 root disk 8, 1 February 27 14:49 /dev/sda1
 BRW RW ---- 1 root disk 8, February 27 14:49 /dev/sda2
 BRW RW ---- 1 root disk 8, February 27, 2016 14:49 / dev / SDB
 BRW RW ---- 1 root disk 8, 32 February 27 14:51 /dev/sdc
 BRW RW ---- 1 root disk 8, 33 February 27 14:51 /dev/sdc1
 BRW RW ---- 1 root disk 8, 34 February 27 14:51 /dev/sdc2

Basic idea of RAID: combine several cheap hard disks into a new hard disk array group by certain combination way, so that it can meet the requirements of high performance hard disk

RAID has three key technologies:
Image: provides data security;
Stripe (block size can also be said to be stripe granularity), which exists to improve I/O performance and provide data concurrency
Data verification: provides data security

Create raid0

[root@centos7-xinsz08 ~]# rpm -qf `which mdadm`
mdadm-4.1-1.el7.x86_64
//Establish
[root@centos7-xinsz08 ~]# mdadm -C -v /dev/md0 -l 0 -n 2 /dev/sdc1 /dev/sdc2
mdadm: chunk size defaults to 512K
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
//See
[root@centos7-xinsz08 ~]# mdadm -D
mdadm: No devices given.
[root@centos7-xinsz08 ~]# mdadm -Ds
ARRAY /dev/md0 metadata=1.2 name=centos7-xinsz08:0 UUID=fa65ca42:f3f9d039:7ee6fad1:1e005f45
[root@centos7-xinsz08 ~]# mdadm -D /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Thu Feb 27 14:57:37 2020
        Raid Level : raid0
        Array Size : 10475520 (9.99 GiB 10.73 GB)
      Raid Devices : 2
     Total Devices : 2
       Persistence : Superblock is persistent

       Update Time : Thu Feb 27 14:57:37 2020
             State : clean 
    Active Devices : 2
   Working Devices : 2
    Failed Devices : 0
     Spare Devices : 0

        Chunk Size : 512K

Consistency Policy : none

              Name : centos7-xinsz08:0  (local to host centos7-xinsz08)
              UUID : fa65ca42:f3f9d039:7ee6fad1:1e005f45
            Events : 0

    Number   Major   Minor   RaidDevice State
       0       8       33        0      active sync   /dev/sdc1
       1       8       34        1      active sync   /dev/sdc2

Remarks:
chunk value:
The stripe size is divided into many "chunks". If the Chunk size is set too small, it will increase the number of blocks occupied

Save configuration information

[root@centos7-xinsz08 ~]# mdadm -Ds
ARRAY /dev/md0 metadata=1.2 name=centos7-xinsz08:0 UUID=fa65ca42:f3f9d039:7ee6fad1:1e005f45
[root@centos7-xinsz08 ~]# mdadm -Ds > /etc/mdadm.conf
[root@centos7-xinsz08 ~]# cat !$
cat /etc/mdadm.conf
ARRAY /dev/md0 metadata=1.2 name=centos7-xinsz08:0 UUID=fa65ca42:f3f9d039:7ee6fad1:1e005f45
[root@centos7-xinsz08 ~]# 

Create partition on raid 0

[root@centos7-xinsz08 ~]# fdisk /dev/md0
 Welcome to fdisk (util Linux 2.23.2).

Changes stay in memory until you decide to write them to disk.
Think twice before using the write command.

Device does not contain a recognized partition table
 Use disk identifier 0xa26b921f to create a new DOS disk label.

Command (enter m for help): n
Partition type:
   p   primary (0 primary, 0 extended, 4 free)
   e   extended
Select (default p): 
Using default response p
 Partition number (1-4, default 1): 1
 Start sector (2048-20951039, default 2048):
The default value 2048 will be used
 Last sector, + sector or +size{K,M,G} (2048-20951039, default is 20951039): + 2G
 Partition 1 is set to Linux type and size is set to 2 GiB

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

Calling ioctl() to re-read partition table.
Synchronizing disks.
[root@centos7-xinsz08 ~]# ll /dev/md*
BRW RW ---- 1 root disk 9, February 27, 0 15:17 / dev / md0
 BRW RW ---- 1 root disk 259, January February 27 15:17 /dev/md0p1

Format partition and mount

[root@centos7-xinsz08 ~]# mkfs.xfs /dev/md0p1
meta-data=/dev/md0p1             isize=512    agcount=8, agsize=65408 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0, sparse=0
data     =                       bsize=4096   blocks=523264, imaxpct=25
         =                       sunit=128    swidth=256 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal log           bsize=4096   blocks=2560, version=2
         =                       sectsz=512   sunit=8 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
[root@centos7-xinsz08 ~]# 
[root@centos7-xinsz08 ~]# mkdir /raid0
[root@centos7-xinsz08 ~]# mount /dev/md0p1 /raid0/
[root@centos7-xinsz08 ~]# df -h |tail -1
/dev/md0p1               2.0G   33M  2.0G    2% /raid0
[root@centos7-xinsz08 ~]# 

Set up auto mount after power on

[root@centos7-xinsz08 ~]# umount /raid0/

[root@centos7-xinsz08 ~]# df -h  |tail -1
tmpfs                    378M     0  378M    0% /run/user/0
[root@centos7-xinsz08 ~]# mount  -a
[root@centos7-xinsz08 ~]# df -h
//File system capacity used% free used% mount point
devtmpfs                 1.9G     0  1.9G    0% /dev
tmpfs                    1.9G     0  1.9G    0% /dev/shm
tmpfs                    1.9G   13M  1.9G    1% /run
tmpfs                    1.9G     0  1.9G    0% /sys/fs/cgroup
/dev/mapper/centos-root   17G  4.7G   13G   28% /
/dev/sda1               1014M  219M  796M   22% /boot
tmpfs                    378M   12K  378M    1% /run/user/42
tmpfs                    378M     0  378M    0% /run/user/0
[root@centos7-xinsz08 ~]# vim /etc/fstab
/dev/md0p1   /raid0   xfs  defaults 0 0
[root@centos7-xinsz08 ~]# mount -a
[root@centos7-xinsz08 ~]# df -h
//File system capacity used% free used% mount point
/dev/md0p1               2.0G   33M  2.0G    2% /raid0