独立硬盘冗余阵列（RAID, Redundant Array of Independent Disks），简称磁盘阵列。利用虚拟化存储技术把多个硬盘组合起来，成为一个或多个硬盘阵列组，目的为提升性能或资料冗余，或是两者同时提升。

RAID 0

RAID 0将两个以上的磁盘并联起来，成为一个大容量的磁盘。在存放数据时，分段后分散存储在这些磁盘中，因为读写时都可以并行处理，所以在所有的级别中，RAID 0的速度是最快的。但是RAID 0既没有冗余功能，也不具备容错能力，如果一个磁盘（物理）损坏，所有数据都会丢失。

创建RAID 0

借助mdadm工具将sdc与sdd磁盘构建成RAID 0

[ecx@evm-ci0603f1ccmlom5ne6e0 ~]$ lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda      8:0    0   80G  0 disk 
└─sda1   8:1    0   80G  0 part /
sdb      8:16   0 1000G  0 disk /data
sdc      8:32   0  100G  0 disk 
sdd      8:48   0  100G  0 disk 
sr0     11:0    1    1M  0 rom
[ecx@evm-ci0603f1ccmlom5ne6e0 ~]$ mdadm -Cv -l0 -c64 -n2 /dev/md0 /dev/sd{c,d}
-bash: mdadm: command not found

提示没有mdadm工具，进行mdadm安装

[ecx@evm-ci0603f1ccmlom5ne6e0 ~]$ sudo yum -y install mdadm

创建raid 0

[root@evm-ci0603f1ccmlom5ne6e0 ~]# mdadm -Cv -l0 -c64 -n2 /dev/md0 /dev/sd{c,d}
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
[root@evm-ci0603f1ccmlom5ne6e0 ~]# cat /proc/mdstat
Personalities : [raid0] 
md0 : active raid0 sdd[1] sdc[0]
      209582080 blocks super 1.2 64k chunks
      
unused devices: <none>

创建文件系统与挂载点

[root@evm-ci0603f1ccmlom5ne6e0 ~]# mkfs.xfs /dev/md0
meta-data=/dev/md0               isize=512    agcount=16, agsize=3274704 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0, sparse=0
data     =                       bsize=4096   blocks=52395264, imaxpct=25
         =                       sunit=16     swidth=32 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal log           bsize=4096   blocks=25584, version=2
         =                       sectsz=512   sunit=16 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0

[root@evm-ci0603f1ccmlom5ne6e0 ~]# mkdir -p /raid0
[root@evm-ci0603f1ccmlom5ne6e0 ~]# mount /dev/md0 /raid0
[root@evm-ci0603f1ccmlom5ne6e0 ~]# df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1        80G  1.9G   79G   3% /
devtmpfs         16G     0   16G   0% /dev
tmpfs            16G     0   16G   0% /dev/shm
tmpfs            16G   17M   16G   1% /run
tmpfs            16G     0   16G   0% /sys/fs/cgroup
/dev/sdb       1000G  134M 1000G   1% /data
tmpfs           3.2G     0  3.2G   0% /run/user/1001
/dev/md0        200G   33M  200G   1% /raid0

加入重启配置

[root@evm-ci0603f1ccmlom5ne6e0 ~]# vi /etc/fstab

#
# /etc/fstab
# Created by anaconda on Thu Aug  8 12:37:33 2019
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
UUID=3ef2b806-efd7-4eef-aaa2-2584909365ff /                       xfs     defaults        0 0
/dev/md0                                  /raid0                  xfs     defaults        0 0 

读写测试

写测试

[root@evm-ci0603f1ccmlom5ne6e0 ~]# time dd if=/dev/zero of=/raid0/10GWrite bs=1k count=10000000
10000000+0 records in
10000000+0 records out
10240000000 bytes (10 GB) copied, 31.0588 s, 330 MB/s

real    0m31.061s
user    0m1.110s
sys     0m20.009s

读测试

[root@evm-ci0603f1ccmlom5ne6e0 ~]# time dd if=/raid0/10GWrite of=/dev/null bs=1k
10000000+0 records in
10000000+0 records out
10240000000 bytes (10 GB) copied, 5.83972 s, 1.8 GB/s

real    0m5.841s
user    0m0.777s
sys     0m5.064s

扩展RAID 0

查看当前磁盘阵列配置

[root@evm-ci0603f1ccmlom5ne6e0 ~]# mdadm --detail /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Thu Jun  8 10:28:41 2023
        Raid Level : raid0
        Array Size : 209582080 (199.87 GiB 214.61 GB)
      Raid Devices : 2
     Total Devices : 2
       Persistence : Superblock is persistent
...

添加新磁盘

[root@evm-ci0603f1ccmlom5ne6e0 ~]# mdadm --add /dev/md0 /dev/sdb
mdadm: Cannot open /dev/sdb: Device or resource busy

解挂再次添加

[root@evm-ci0603f1ccmlom5ne6e0 ~]# umount /dev/sdb /data
umount: /data: not mounted
[root@evm-ci0603f1ccmlom5ne6e0 ~]# mdadm --add /dev/md0 /dev/sdb
mdadm: add new device failed for /dev/sdb as 2: Invalid argument

使用grow命令，RAID 0变成了RAID 4

[root@evm-ci0603f1ccmlom5ne6e0 ~]# mdadm --grow /dev/md0 --level=0 --raid-devices=3 --backup-file=/data1/backup --add /dev/sdb
mdadm: level of /dev/md0 changed to raid4
mdadm: added /dev/sdb
[root@evm-ci0603f1ccmlom5ne6e0 ~]# mdadm --detail /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Thu Jun  8 10:28:41 2023
        Raid Level : raid4
        Array Size : 209582080 (199.87 GiB 214.61 GB)
     Used Dev Size : 104791040 (99.94 GiB 107.31 GB)
      Raid Devices : 4
     Total Devices : 3
       Persistence : Superblock is persistent

       Update Time : Fri Jun  9 03:15:52 2023
             State : clean, FAILED, reshaping 
    Active Devices : 2
   Working Devices : 3
    Failed Devices : 0
     Spare Devices : 1

此时磁盘仍然是200G

[root@evm-ci0603f1ccmlom5ne6e0 ~]# df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1        80G  2.0G   79G   3% /
devtmpfs         16G     0   16G   0% /dev
tmpfs            16G     0   16G   0% /dev/shm
tmpfs            16G   25M   16G   1% /run
tmpfs            16G     0   16G   0% /sys/fs/cgroup
/dev/md0        200G   33M  200G   1% /raid0
tmpfs           3.2G     0  3.2G   0% /run/user/1001
tmpfs           3.2G     0  3.2G   0% /run/user/0

执行mdadm --detail /dev/md0，发现raid0处于reshape status状态。

[root@evm-ci0603f1ccmlom5ne6e0 ~]# cat /proc/mdstat 
Personalities : [raid0] [raid6] [raid5] [raid4] 
md0 : active raid4 sdb[3] sdd[1] sdc[0]
      209582080 blocks super 1.2 level 4, 64k chunk, algorithm 5 [4/3] [UU__]
      [==>..................]  reshape = 12.4% (13032960/104791040) finish=1151.1min speed=1328K/sec
      
unused devices: <none>