Linux 软RAID---mdadm

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一 .RAID 建立

mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb{1,2}

mdadm --create /dev/md0 --level=5 --raid-devices=2 /dev/sdb{1,2}

添加热备 :

mdadm --create /dev/md0 --add /dev/sdb3

创建 raid10

# mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb{1,2}

# mdadm --create /dev/md1 --level=1 --raid-devices=2 /dev/sdb{3,4} -a yes

# mdadm --create /dev/md2 --level=10 --raid-devices=2 /dev/md{0,1} -a yes

二 . /proc/mdstat

[root@station20 ~]# cat /proc/mdstat

Personalities : [raid1] [raid6] [raid5] [raid4]

md1 : active raid5 sdb10[3] sdb9[1] sdb8[0]

196224 blocks level 5, 64k chunk, algorithm 2 [3/2] [UU_]

[===============>.....] recovery = 79.1% (78592/98112) finish=0.0min speed=4136K/sec

md0 : active raid1 sdb7[1] sdb6[0]

98112 blocks [2/2] [UU]

bitmap: 0/12 pages [0KB], 4KB chunk

unused devices: <none>

三 . 位图 : --bitmap=internal

原理描述：

在 mdadm 操作中， bitmap 用于记录 RAID 阵列从上次同步之后更改的部分，即记录 RAID 阵列有多少个块已经同步 (resync) 。 RAID 阵列会定期将信息写入到 bitmap 中。在一般情况下，磁盘阵列在重启之后会有一个完整的同步过程。如果有 bitmap ，那么只有被修改后的数据才会被同步。在另一种情况下，如果阵列一块磁盘被取出， bitmap 不会被清除，当这块磁盘重新加入阵列时，同样只会同步改变过的数据。所以 bitmap 能够减少磁盘阵列同步的时间，起到优化 raid1 的作用。 Bitmap 一般写入的位置是磁盘的 metadata 或者我们成为外部的另外，要注意的是， bitmap 只是对 raid1 的功能，对 raid0 等其他设备来说是没有意义的 .

注意 : 此功能只对 RAID1 有效

Example: mdadm --create /dev/md0 --level=1 --raid-devices=2 -a yes -b internal

在已存在的 RAID1 上启用视图

mdadm --grow /dev/md0 --bitmap=internal

四 . 共享热备盘及邮件通知

[root@server109 ~]# mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sda{5,6} -a yes -b internal

[root@server109 ~]# mdadm --create /dev/md1 --level=5 --raid-devices=3 /dev/sda{7,8,9} -a yes

[root@server109 ~]# mdadm /dev/md0 --add /dev/sda10

[root@server109 ~]# cat /proc/mdstat

Personalities : [raid1] [raid6] [raid5] [raid4]

md1 : active raid5 sda9[2] sda8[1] sda7[0]

196736 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]

md0 : active raid1 sda10[2](S) sda6[1] sda5[0]

98368 blocks [2/2] [UU]

bitmap: 0/13 pages [0KB], 4KB chunk

unused devices: <none>

[root@server109 ~]# mdadm --examine --scan > /etc/mdadm.conf

[root@server109 ~]# cat /etc/mdadm.conf

ARRAY /dev/md1 level=raid5 num-devices=3 UUID=891d6352:a0a4efff:4f162d90:c3500453

ARRAY /dev/md0 level=raid1 num-devices=2 UUID=b070e059:fe2cf975:aac92394:e103a46d

spares=1

可以实现热备共享及邮件通知的配置文件如下 ( 直接修改 mdadm.conf):

[root@server109 ~]# cat /etc/mdadm.conf

## Share Host Spares

ARRAY /dev/md1 level=raid5 num-devices=3 UUID=891d6352:a0a4efff:4f162d90:c3500453 spare-group=1

ARRAY /dev/md0 level=raid1 num-devices=2 UUID=b070e059:fe2cf975:aac92394:e103a46d spare-group=1

spares=1

## Mail Notification

MAILFROM root@localhost ## 邮件发出 , 不写默认为 root

MAILADDR raider@localhost ## 邮件接收

[root@server109 ~]# /etc/init.d/mdmonitor start

[root@server109 ~]# useradd raider

[root@server109 ~]# echo redhat | passwd --stdin raider

[root@server109 ~]# cat /proc/mdstat

Personalities : [raid1] [raid6] [raid5] [raid4]

md1 : active raid5 sda9[2] sda8[1] sda7[0]

196736 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]

md0 : active raid1 sda10[2](S) sda6[1] sda5[0]

98368 blocks [2/2] [UU]

bitmap: 0/13 pages [0KB], 4KB chunk

unused devices: <none>

[root@server109 ~]# mdadm /dev/md1 -f /dev/sda7 -r /dev/sda7

mdadm: set /dev/sda7 faulty in /dev/md1

mdadm: hot removed /dev/sda7

[root@server109 ~]# cat /proc/mdstat

Personalities : [raid1] [raid6] [raid5] [raid4]

md1 : active raid5 sda10[3] sda9[2] sda8[1]

196736 blocks level 5, 64k chunk, algorithm 2 [3/2] [_UU]

[====>................] recovery = 24.7% (25472/98368) finish=0.1min speed=6368K/sec

md0 : active raid1 sda6[1] sda5[0]

98368 blocks [2/2] [UU]

bitmap: 0/13 pages [0KB], 4KB chunk

[root@server109 ~]# mail -u raider

Mail version 8.1 6/6/93. Type ? for help.

"/var/mail/raider": 1 message 1 new

>N 1 root@server109.examp Tue Jan 4 04:28 35/1262 "Fail event on /dev/md1:server109.example.com"

& 1

Message 1:

From root@server109.example.com Tue Jan 4 04:28:48 2011

Date: Tue, 4 Jan 2011 04:28:47 +0100

From: root@server109.example.com

To: raider@server109.example.com

Subject: Fail event on /dev/md1:server109.example.com

.........................

A Fail event had been detected on md device /dev/md1.

It could be related to component device /dev/sda7.

...............................

五 .RAID 扩展 --grow

如果某天 RAID 空间不够用了 , 如何增加 RAID 的空间呢 ?

The steps for adding a new disk are:

1. Add the new disk to the active 3-device RAIDS (starts as a spare):

mdadm -add /d ev /mdO /d ev /hda8

2 Reshape the RAID 5 :

mdadm --grow /dev/md0 --raid-devices=4

3. Monitor the reshaping process and estimated time to fi ni sh:

watch -n 1 'cat /proc/mdstat'

4. Expand the FS to fill the new space:

resize2fs /dev/md0

[root@server109 ~]# mdadm /dev/md1 --add /dev/sda1 1

[root@server109 ~]# mdadm /dev/md1 --grow --raid-devices= 5

[root@server109 ~]# cat /proc/mdstat

Personalities : [raid1] [raid6] [raid5] [raid4]

md1 : active raid5 sda11[4] sda7[3] sda10[0] sda9[2] sda8[1]

295104 blocks super 0.91 level 5, 64k chunk, algorithm 2 [5/5] [UUUUU]

[>....................] reshape = 2.0% (2812/98368) finish=1.0min speed=1406K/sec

md0 : active raid1 sda6[1] sda5[0]

98368 blocks [2/2] [UU]

bitmap: 0/13 pages [0KB], 4KB chunk

unused devices: <none>

[root@server109 ~]# resize2fs /dev/md1

六 . RAID 恢复

OS 为独立硬盘 , 数据存储在一个 RAID5 上 , 重新安装 OS 后如何恢复 RAID 呢 ?

[root@server109 ~]# mdadm --examine /dev/sda8

/dev/sda8:

Magic : a92b4efc

Version : 0.90.00

UUID : 891d6352:a0a4efff:4f162d90:c3500453

Creation Time : Tue Jan 4 04:18:45 2011

Raid Level : raid5

Used Dev Size : 98368 (96.08 MiB 100.73 MB)

Array Size : 393472 (384.31 MiB 402.92 MB)

Raid Devices : 5

Total Devices : 5

Preferred Minor : 1

Update Time : Tue Jan 4 05:17:52 2011

State : clean

Active Devices : 5

Working Devices : 5

Failed Devices : 0

Spare Devices : 0

Checksum : 7f9b882a - correct

Events : 206

Layout : left-symmetric

Chunk Size : 64K

Number Major Minor RaidDevice State

this 1 8 8 1 active sync /dev/sda8

0 0 8 10 0 active sync /dev/sda10

1 1 8 8 1 active sync /dev/sda8

2 2 8 9 2 active sync /dev/sda9

3 3 8 7 3 active sync /dev/sda7

4 4 8 11 4 active sync /dev/sda11

[root@server109 ~]# mdadm -A /dev/md1 /dev/sda{7,8,9,10,11}

mdadm: /dev/md1 has been started with 5 drives.

[root@server109 ~]# mount /dev/md1 /mnt/

七 .Raid 重命名

rename / dev / md 1 to / dev / md3

[root@server109 ~]# umount /mnt/

[root@server109 ~]# mdadm --stop /dev/md1

[root@server109 ~]# mdadm --assemble /dev/md3 --super-minor=1 --update=super-minor /dev/sda{7,8,9,10,11}

说明 : --super-minor=1 这里的 "1" 与 /dev/md1 一至 , 如果重命令的是 /dev/md0, 那这里就是 --super-minor=0