mdadm使用详解及RAID 5简单分析

布满荆棘的人生 2022-08-08 14:42 713阅读 0赞

**本文是** [《**用raidtools创建Linux Soft RAID**][raidtools_Linux Soft RAID]》 **的续篇，关于如何使用raidtools在Linux下创建软RAID请参考原文**

**关于RAID原理、常用的RAID级别和参数以及各种RAID之间的对比可参考以下链接：**  
  
**RAID Calculator** ( [en][] | [ch][] ) **&** **RAID Summary Comparison** ( [en][en 1] | [ch][ch 1] ) beta @ [my googlepage][]

**★什么是mdadm?**

mdadm是 multiple devices admin的简称，它是Linux下的一款标准的软件 RAID 管理工具，作者是 [Neil Brown][]。

**★为什么选择mdadm?**

我们知道 raidtools是Linux下一款经典的用于管理软件 RAID 的工具，但是因为配置 /etc/raidtab比较繁琐，而且其功能有限，所以现在越来越多的人选择mdadm。  
  
**mdadm 和 raidtools 主要有以下几点不同**：

*  mdadm能够诊断、监控和收集详细的阵列信息  
    
 *  mdadm是一个单独集成化的程序而不是一些分散程序的集合，因此对不同RAID管理命令有共通的语法  
    
 *  mdadm能够执行几乎所有的功能而不需要配置文件(也没有默认的配置文件)  
    
 *  当然，如果需要一个配置文件，mdadm将帮助管理它的内容

**★准备工作**

**QUOTE:**

首先我们在虚拟机中添加四块SCSI硬盘(我们仍然直接使用只有一个分区的硬盘( sdb、sdc、sdd、sde)来作为RAID设备的成员，每个盘大小为 8G)并分区格式化，具体步骤可参考 [**用raidtools创建Linux Soft RAID**][raidtools_Linux Soft RAID]，这里从略

**★下载、安装mdadm**

你可以到mdadm的 [官方网站][Neil Brown]( [http://www.cse.unsw.edu.au/~neilb/source/mdadm/][Neil Brown])下载最新的压缩包。目前最新的版本是 mdadm-2.6.2( [LATEST.tgz][] or [mdadm-2.6.2.tgz][])。 推荐下载tgz格式的压缩包自行编译然后安装mdadm和它的文档、手册和示例文件。  
  
安装步骤如下：

login as: eric4ever  
eric4ever@192.168.254.30's password:  
Last login: Thu May 24 10:59:06 2007 from 192.168.254.1  
\[root@localhost eric4ever\]\# ls -lh  
total 208K  
\-rw-r--r-- 1 root root 201K May 24 11:01 LATEST.tgz  
\[root@localhost eric4ever\]\# tar zxvf LATEST.tgz  
mdadm-2.6.2/  
mdadm-2.6.2/mdadm.conf-example  
mdadm-2.6.2/misc/  
mdadm-2.6.2/misc/syslog-events  
mdadm-2.6.2/md\_u.h  
mdadm-2.6.2/TODO  
mdadm-2.6.2/ANNOUNCE-2.0  
mdadm-2.6.2/kernel-patch-2.6.18  
mdadm-2.6.2/Query.c  
mdadm-2.6.2/ReadMe.c  
mdadm-2.6.2/super0.c  
mdadm-2.6.2/SHA1.c  
mdadm-2.6.2/ANNOUNCE-2.6  
mdadm-2.6.2/ANNOUNCE-2.6.1  
mdadm-2.6.2/Monitor.c  
mdadm-2.6.2/md\_p.h  
mdadm-2.6.2/mdassemble.c  
mdadm-2.6.2/mdadm.h  
mdadm-2.6.2/mdadm.spec  
mdadm-2.6.2/mdadm.c  
mdadm-2.6.2/Assemble.c  
mdadm-2.6.2/Kill.c  
mdadm-2.6.2/ANNOUNCE-2.1  
mdadm-2.6.2/pwgr.c  
mdadm-2.6.2/Incremental.c  
mdadm-2.6.2/mapfile.c  
mdadm-2.6.2/Grow.c  
mdadm-2.6.2/tests/  
mdadm-2.6.2/tests/00raid4  
mdadm-2.6.2/tests/05r6-bitmapfile  
mdadm-2.6.2/tests/02r6grow  
mdadm-2.6.2/tests/03r5assem  
mdadm-2.6.2/tests/07testreshape5  
mdadm-2.6.2/tests/05r1-internalbitmap-v1c  
mdadm-2.6.2/tests/02r5grow  
mdadm-2.6.2/tests/05r1-re-add  
mdadm-2.6.2/tests/00raid6  
mdadm-2.6.2/tests/01r5fail  
mdadm-2.6.2/tests/06update-uuid  
mdadm-2.6.2/tests/05r1-bitmapfile  
mdadm-2.6.2/tests/02r1grow  
mdadm-2.6.2/tests/05r1-n3-bitmapfile  
mdadm-2.6.2/tests/06wrmostly  
mdadm-2.6.2/tests/05r1-re-add-nosuper  
mdadm-2.6.2/tests/00raid5  
mdadm-2.6.2/tests/03r5assemV1  
mdadm-2.6.2/tests/00multipath  
mdadm-2.6.2/tests/05r1-internalbitmap-v1b  
mdadm-2.6.2/tests/06name  
mdadm-2.6.2/tests/05r1-grow-internal-1  
mdadm-2.6.2/tests/01r1fail  
mdadm-2.6.2/tests/00raid0  
mdadm-2.6.2/tests/05r1-grow-external  
mdadm-2.6.2/tests/06r5swap  
mdadm-2.6.2/tests/07autodetect  
mdadm-2.6.2/tests/05r1-internalbitmap  
mdadm-2.6.2/tests/02lineargrow  
mdadm-2.6.2/tests/00raid1  
mdadm-2.6.2/tests/testdev  
mdadm-2.6.2/tests/05r5-internalbitmap  
mdadm-2.6.2/tests/00raid10  
mdadm-2.6.2/tests/ToTest  
mdadm-2.6.2/tests/05r5-bitmapfile  
mdadm-2.6.2/tests/04r0update  
mdadm-2.6.2/tests/02r1add  
mdadm-2.6.2/tests/03r0assem  
mdadm-2.6.2/tests/check  
mdadm-2.6.2/tests/06sysfs  
mdadm-2.6.2/tests/05r1-grow-internal  
mdadm-2.6.2/tests/04r1update  
mdadm-2.6.2/tests/00linear  
mdadm-2.6.2/tests/05r1-internalbitmap-v1a  
mdadm-2.6.2/mdassemble.8  
mdadm-2.6.2/restripe.c  
mdadm-2.6.2/Manage.c  
mdadm-2.6.2/md.4  
mdadm-2.6.2/ANNOUNCE-2.5  
mdadm-2.6.2/ChangeLog  
mdadm-2.6.2/Examine.c  
mdadm-2.6.2/ANNOUNCE-2.5.1  
mdadm-2.6.2/sha1.h  
mdadm-2.6.2/inventory  
mdadm-2.6.2/ANNOUNCE-2.3  
mdadm-2.6.2/sha1.c  
mdadm-2.6.2/raid5extend.c  
mdadm-2.6.2/bitmap.c  
mdadm-2.6.2/ANNOUNCE-2.6.2  
mdadm-2.6.2/ANNOUNCE-2.5.3  
mdadm-2.6.2/dlink.c  
mdadm-2.6.2/md5.h  
mdadm-2.6.2/config.c  
mdadm-2.6.2/mdadm.conf.5  
mdadm-2.6.2/mkinitramfs  
mdadm-2.6.2/swap\_super.c  
mdadm-2.6.2/bitmap.h  
mdadm-2.6.2/test  
mdadm-2.6.2/mdopen.c  
mdadm-2.6.2/ANNOUNCE-2.5.5  
mdadm-2.6.2/Create.c  
mdadm-2.6.2/kernel-patch-2.6.19  
mdadm-2.6.2/mdadm.8  
mdadm-2.6.2/ANNOUNCE-2.2  
mdadm-2.6.2/ANNOUNCE-2.5.4  
mdadm-2.6.2/COPYING  
mdadm-2.6.2/sysfs.c  
mdadm-2.6.2/super1.c  
mdadm-2.6.2/Makefile  
mdadm-2.6.2/util.c  
mdadm-2.6.2/INSTALL  
mdadm-2.6.2/mdstat.c  
mdadm-2.6.2/ANNOUNCE-2.4.1  
mdadm-2.6.2/dlink.h  
mdadm-2.6.2/ANNOUNCE-2.5.6  
mdadm-2.6.2/ANNOUNCE-2.3.1  
mdadm-2.6.2/makedist  
mdadm-2.6.2/kernel-patch-2.6.18.6  
mdadm-2.6.2/ANNOUNCE-2.5.2  
mdadm-2.6.2/ANNOUNCE-2.4-pre1  
mdadm-2.6.2/Detail.c  
mdadm-2.6.2/README.initramfs  
mdadm-2.6.2/ANNOUNCE-2.4  
mdadm-2.6.2/Build.c  
\[root@localhost eric4ever\]\# ls -lh  
total 212K  
\-rw-r--r-- 1 root root 201K May 24 11:01 LATEST.tgz  
drwxr-xr-x 4 1000 1000 4.0K May 21 12:25 mdadm-2.6.2  
  
\[root@localhost eric4ever\]\# cd mdadm-2.6.2/  
  
\[root@localhost mdadm-2.6.2\]\# make install

<table style="color:rgb(0,0,0); font-family:Arial; font-size:14px; line-height:26px; border-collapse:collapse; width:553px; height:1492px"> 
 <tbody> 
 <tr> 
 <td> <code>gcc&nbsp;-Wall&nbsp;-Werror&nbsp;-Wstrict-prototypes&nbsp;-ggdb&nbsp;-DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o mdadm.o mdadm.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o config.o config.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o mdstat.o mdstat.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o ReadMe.o ReadMe.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o util.o util.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o Manage.o Manage.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o Assemble.o Assemble.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o Build.o Build.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o Create.o Create.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o Detail.o Detail.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o Examine.o Examine.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o Grow.o Grow.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o Monitor.o Monitor.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o dlink.o dlink.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o Kill.o Kill.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o Query.o Query.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o Incremental.o Incremental.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o mdopen.o mdopen.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o super0.o super0.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o super1.o super1.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o bitmap.o bitmap.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o restripe.o restripe.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -c -o sysfs.o sysfs.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t"/" -DCONFFILE=/"/etc/mdadm.conf/" -DCONFFILE2=/"/etc/mdadm/mdadm.conf/" -DHAVE_STDINT_H -o sha1.o -c sha1.c gcc -Wall -Werror -Wstrict-prototypes -ggdb -DSendmail=/""/usr/sbin/sendmail-t</code> /usr/bin/install -D -m 644 mdadm.8 /usr/share/man/man8/mdadm.8 /usr/bin/install -D -m 644 md.4 /usr/share/man/man4/md.4 /usr/bin/install -D -m 644 mdadm.conf.5 /usr/share/man/man5/mdadm.conf.5 /usr/bin/install -D &nbsp;-m 755 mdadm /sbin/mdadm </td> 
 </tr> 
 </tbody> 
</table>

\[root@localhost mdadm-2.6.2\]\#  
  
你也可以使用基于RPM的发布包，你可以从 [这里][Link 1] 下载，不过最新的RPM为 2.6-1 版本：

\[root@localhost mdadm-2.6.2\]\# rpm -ihv mdadm-1.4.0-1.i386.rpm  
  
  
**★mdadm简介**

我们可以使用 man mdadm命令来查看mdadm的帮助信息：

\[root@localhost mdadm-2.6.2\]\# man mdadm

关于 man mdadm的详细信息请查看 [4楼][4]

**☆mdadm用法  
  
基本语法**：

mdadm \[mode\] <raid-device> \[options\] <component-devices>

**目前支持**：

LINEAR, RAID0(striping), RAID1(mirroring), RAID4, RAID5, RAID6, RAID10, MULTIPATH和FAULTY

**模式(7种)：**

*  Assemble：加入一个以前定义的阵列  
    
 *  Build：创建一个没有超级块的阵列  
    
 *  Create：创建一个新的阵列，每个设备具有超级块  
    
 *  Manage： 管理阵列(如添加和删除)  
    
 *  Misc：允许单独对阵列中的某个设备进行操作(如停止阵列)  
    
 *  Follow or Monitor:监控RAID的状态  
    
 *  Grow：改变RAID的容量或阵列中的设备数目

**选项：**  
\-A, --assemble：加入一个以前定义的阵列  
\-B, --build：创建一个没有超级块的阵列(Build a legacy array without superblocks.)  
\-C, --create：创建一个新的阵列  
\-F, --follow, --monitor：选择监控(Monitor)模式  
\-G, --grow：改变激活阵列的大小或形态  
\-I, --incremental：添加一个单独的设备到合适的阵列，并可能启动阵列  
\--auto-detect：请求内核启动任何自动检测到的阵列  
\-h, --help：帮助信息，用在以上选项后，则显示该选项信息  
\--help-options：显示更详细的帮助  
\-V, --version：打印mdadm的版本信息  
\-v, --verbose：显示细节  
\-b, --brief：较少的细节。用于 --detail 和 --examine 选项  
\-Q, --query：查看一个device，判断它为一个 md device 或是 一个 md 阵列的一部分  
\-D, --detail：打印一个或多个 md device 的详细信息  
\-E, --examine：打印 device 上的 md superblock 的内容  
\-c, --config= ：指定配置文件，缺省为 /etc/mdadm.conf  
\-s, --scan：扫描配置文件或 /proc/mdstat以搜寻丢失的信息。配置文件/etc/mdadm.conf  
  
  
  
**★使用mdadm创建RAID5**

Create ( mdadm --create)模式用来创建一个新的阵列。 在这里我们首先使用 mdadm --create --help查看一下帮助：

\[root@localhost mdadm-2.6.2\]\# mdadm --create --help  
Usage: mdadm --create device -chunk=X --level=Y --raid-devices=Z devices  
  
This usage will initialise a new md array, associate some  
devices with it, and activate the array. In order to create an  
array with some devices missing, use the special word 'missing' in  
place of the relevant device name.  
  
Before devices are added, they are checked to see if they already contain  
raid superblocks or filesystems. They are also checked to see if  
the variance in device size exceeds 1%.  
If any discrepancy is found, the user will be prompted for confirmation  
before the array is created. The presence of a '--run' can override this  
caution.  
  
If the --size option is given then only that many kilobytes of each  
device is used, no matter how big each device is.  
If no --size is given, the apparent size of the smallest drive given  
is used for raid level 1 and greater, and the full device is used for  
other levels.  
  
Options that are valid with --create (-C) are:  
\--bitmap= : Create a bitmap for the array with the given filename  
\--chunk= -c : chunk size of kibibytes  
\--rounding= : rounding factor for linear array (==chunk size)  
\--level= -l : raid level: 0,1,4,5,6,linear,multipath and synonyms  
\--parity= -p : raid5/6 parity algorithm: \{left,right\}-\{,a\}symmetric  
\--layout= : same as --parity  
\--raid-devices= -n : number of active devices in array  
\--spare-devices= -x: number of spares (eXtras) devices in initial array  
\--size= -z : Size (in K) of each drive in RAID1/4/5/6/10 - optional  
\--force -f : Honour devices as listed on command line. Don't  
: insert a missing drive for RAID5.  
\--run -R : insist of running the array even if not all  
: devices are present or some look odd.  
\--readonly -o : start the array readonly - not supported yet.  
\--name= -N : Textual name for array - max 32 characters  
\--bitmap-chunk= : bitmap chunksize in Kilobytes.  
\--delay= -d : bitmap update delay in seconds.

接下来我们使用 mdadm创建在/dev/md0上创建一个由 sdb、sdc、sdd3块盘组成(另外1块盘 sde为热备)的RAID5：

\[root@localhost mdadm-2.6.2\]\# mdadm --create --verbose /dev/md0 --level=raid5 --raid-devices=3 /dev/sdb /dev/sdc /dev/sdd --spare-devices=1 /dev/sde  
mdadm: layout defaults to left-symmetric  
mdadm: chunk size defaults to 64K  
mdadm: size set to 8388544K  
mdadm: array /dev/md0 started.

每个 mdadm的选项都有一个 缩写的形式，例如，上面我们创建RAID 5的命令可以使用下列的缩写形式：

\[root@localhost mdadm-2.6.2\]\# mdadm -Cv /dev/md0 -l5 -n3 /dev/sdb /dev/sdc /dev/sdd -x1 /dev/sde

二者的效果是相同的。

**★查看RAID状态**

接下来我们使用 cat /proc/mdstat命令来查看一下RAID的状态，我们也可以利用 watch命令来每隔一段时间刷新 /proc/mdstat的输出。使用 CTRL+C可以取消。

\[root@localhost mdadm-2.6.2\]\# watch -n 10 'cat /proc/mdstat' 
Every 10s: cat /proc/mdstat Thu May 24 11:53:46 2007 
 
Personalities : \[raid5\] 
read\_ahead 1024 sectors 
md0 : active raid5 sdd\[4\] sde\[3\] sdc\[1\] sdb\[0\] 
16777088 blocks level 5, 64k chunk, algorithm 2 \[3/2\] \[UU\_\] 
\[====>................\] recovery = 24.0% (2016364/8388544) finish=10.2min 
speed=10324K/sec 
unused devices: <none> 
\[root@localhost mdadm-2.6.2\]\#

接下来我们为阵列创建文件系统：

\[root@localhost mdadm-2.6.2\]\# mkfs.ext3 /dev/md0  
mke2fs 1.34 (25-Jul-2003)  
Filesystem label=  
OS type: Linux  
Block size=4096 (log=2)  
Fragment size=4096 (log=2)  
2097152 inodes, 4194272 blocks  
209713 blocks (5.00%) reserved for the super user  
First data block=0  
128 block groups  
32768 blocks per group, 32768 fragments per group  
16384 inodes per group  
Superblock backups stored on blocks:  
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,  
4096000  
  
Writing inode tables: done  
Creating journal (8192 blocks): done  
Writing superblocks and filesystem accounting information: done  
  
This filesystem will be automatically checked every 34 mounts or  
180 days, whichever comes first. Use tune2fs -c or -i to override.  
You have new mail in /var/spool/mail/root

我们尝试向RAID中写入一个test2文件：

\[root@localhost eric4ever\]\# vi test2  
copy succeed!  
eric@tlf  
\[url\]http://eric4ever.googlepages.com/\[/url\]  
done!  
\[root@localhost eric4ever\]\# ls  
LATEST.tgz mdadm-2.6.2 test2  
\[root@localhost eric4ever\]\# mount /dev/md0 /mnt/md0  
\[root@localhost eric4ever\]\# df -lh  
Filesystem Size Used Avail Use% Mounted on  
/dev/sda1 2.9G 1.8G 1.1G 63% /  
/dev/sda3 4.6G 33M 4.3G 1% /opt  
none 125M 0 125M 0% /dev/shm  
/dev/md0 16G 33M 15G 1% /mnt/md0  
\[root@localhost eric4ever\]\# ls /mnt/md0  
lost+found  
\[root@localhost eric4ever\]\# cp ./test2 /mnt/md0  
\[root@localhost eric4ever\]\# ls /mnt/md0  
lost+found test2  
\[root@localhost eric4ever\]\# ls -lh /mnt/md0  
total 20K  
drwx------ 2 root root 16K May 24 11:55 lost+found  
\-rw-r--r-- 1 root root 63 May 24 11:56 test2

使用 mdadm --detail /dev/md0(或 mdadm -D /dev/md0)命令以及 cat /proc/mdstat命令可以查看RAID设备的状态：

\[root@localhost eric4ever\]\# mdadm -D /dev/md0 (或mdadm --detail /dev/md0)  
/dev/md0:  
Version : 00.90.00  
Creation Time : Thu May 24 13:45:35 2007  
Raid Level : raid5  
Array Size : 16777088 (16.00 GiB 17.18 GB)  
Used Dev Size : 8388544 (8.00 GiB 8.59 GB)  
Raid Devices : 3  
Total Devices : 5  
Preferred Minor : 0  
Persistence : Superblock is persistent  
  
Update Time : Thu May 24 13:45:36 2007  
State : active, degraded, recovering  
Active Devices : 2  
Working Devices : 4  
Failed Devices : 1  
Spare Devices : 2  
  
Layout : left-symmetric  
Chunk Size : 64K  
  
Rebuild Status : 16% complete  
  
UUID : 4b15050e:7d0c477d:98ed7d00:0f3c29e4  
Events : 0.2  
  
Number Major Minor RaidDevice State  
0 8 16 0 active sync /dev/sdb  
1 8 32 1 active sync /dev/sdc  
2 0 0 2 removed  
  
3 8 64 3 spare /dev/sde  
4 8 48 4 spare /dev/sdd

通过 mdadm -D命令，我们可以查看RAID的 版本、创建的时间、RAID级别、阵列容量、可用空间、设备数量、超级块、更新时间、各个设备的状态、RAID算法以及块大小等信息，通过上面的信息我们可以看到目前RAID正处于 重建过程之中，进度为 16%，其中 /dev/sdb和 /dev/sdc两块盘已经 同步。使用 watch命令每个30秒刷新一下查看的进度：

\[root@localhost eric4ever\]\# watch -n 30 'cat /proc/mdstat' 
Every 30s: cat /proc/mdstat Thu May 24 13:55:56 2007 
 
Personalities : \[raid5\] 
read\_ahead 1024 sectors 
md0 : active raid5 sdd\[4\] sde\[3\] sdc\[1\] sdb\[0\] 
16777088 blocks level 5, 64k chunk, algorithm 2 \[3/2\] \[UU\_\] 
\[==============>......\] recovery = 72.3% (6067444/8388544) finish=3.7min 
speed=10324K/sec 
unused devices: <none>

当进度进行到 100%时，显示如下：

Every 30s: cat /proc/mdstat Thu May 24 14:00:57 2007 
 
Personalities : \[raid5\] 
read\_ahead 1024 sectors 
md0 : active raid5 sdd\[2\] sde\[3\] sdc\[1\] sdb\[0\] 
16777088 blocks level 5, 64k chunk, algorithm 2 \[3/3\] \[UUU\] 
 
unused devices: <none>

这是我们再使用 mdadm -D命令查看一下：

\[root@localhost eric4ever\]\# mdadm -D /dev/md0 (或mdadm --detail /dev/md0)  
/dev/md0:  
Version : 00.90.00  
Creation Time : Thu May 24 13:45:35 2007  
Raid Level : raid5  
Array Size : 16777088 (16.00 GiB 17.18 GB)  
Used Dev Size : 8388544 (8.00 GiB 8.59 GB)  
Raid Devices : 3  
Total Devices : 5  
Preferred Minor : 0  
Persistence : Superblock is persistent  
  
Update Time : Thu May 24 13:59:48 2007  
State : active  
Active Devices : 3  
Working Devices : 4  
Failed Devices : 1  
Spare Devices : 1  
  
Layout : left-symmetric  
Chunk Size : 64K  
  
UUID : 4b15050e:7d0c477d:98ed7d00:0f3c29e4  
Events : 0.3  
  
Number Major Minor RaidDevice State  
0 8 16 0 active sync /dev/sdb  
1 8 32 1 active sync /dev/sdc  
2 8 48 2 active sync /dev/sdd  
  
3 8 64 3 spare /dev/sde

这时我们可以发现 sdb、sdc、sdd三块盘均已经同步。  
  
一般来说，一个新阵列被创建后我们最好创建一个/etc/mdadm.conf文件。没有该文件在激活阵列时我们就得指定更详细的信息，为方便，我们使用下列命令：

\[root@localhost eric4ever\]\# mdadm --detail --scan  
ARRAY /dev/md0 level=raid5 num-devices=3 spares=1 UUID=4b15050e:7d0c477d:98ed7d00:0f3c29e4  
\[root@localhost eric4ever\]\# mdadm --detail --scan >> /etc/mdadm.conf  
\[root@localhost eric4ever\]\# cat /etc/mdadm.conf  
ARRAY /dev/md0 level=raid5 num-devices=3 spares=1 UUID=4b15050e:7d0c477d:98ed7d00:0f3c29e4

**★启动停止RAID**

使用 \--stop或 \-S命令选项可以停止运行的阵列( **注意：** 停止前必须先umount)：

\[root@localhost eric4ever\]\# umount /mnt/md0  
\[root@localhost eric4ever\]\# mdadm -S /dev/md0 (或mdadm --stop /dev/md0)  
mdadm: stopped /dev/md0

重新启动可以使用：

\[root@localhost eric4ever\]\# mdadm -As /dev/md0  
mdadm: /dev/md0 has been started with 3 drives and 1 spare.

**★模拟故障**

同raidtools一样，mdadm也可以软件模拟故障，命令选项为 \--fail或 \--set-faulty：

\[root@localhost eric4ever\]\# mdadm --set-faulty --help  
Usage: mdadm arraydevice options component devices...  
  
This usage is for managing the component devices within an array.  
The --manage option is not needed and is assumed if the first argument  
is a device name or a management option.  
The first device listed will be taken to be an md array device, and  
subsequent devices are (potential) components of that array.  
  
Options that are valid with management mode are:  
\--add -a : hotadd subsequent devices to the array  
\--remove -r : remove subsequent devices, which must not be active  
\--fail -f : mark subsequent devices a faulty  
\--set-faulty : same as --fail  
\--run -R : start a partially built array  
\--stop -S : deactivate array, releasing all resources  
\--readonly -o : mark array as readonly  
\--readwrite -w : mark array as readwrite  
\[root@localhost eric4ever\]\# mdadm --fail --help  
Usage: mdadm arraydevice options component devices...  
  
This usage is for managing the component devices within an array.  
The --manage option is not needed and is assumed if the first argument  
is a device name or a management option.  
The first device listed will be taken to be an md array device, and  
subsequent devices are (potential) components of that array.  
  
Options that are valid with management mode are:  
\--add -a : hotadd subsequent devices to the array  
\--remove -r : remove subsequent devices, which must not be active  
\--fail -f : mark subsequent devices a faulty  
\--set-faulty : same as --fail  
\--run -R : start a partially built array  
\--stop -S : deactivate array, releasing all resources  
\--readonly -o : mark array as readonly  
\--readwrite -w : mark array as readwrite

接下来我们模拟 /dev/sdb故障：

\[root@localhost eric4ever\]\# mdadm --manage --set-faulty /dev/md0 /dev/sdb  
mdadm: set /dev/sdb faulty in /dev/md0

查看一下系统日志，如果你配置了冗余磁盘，可能会显示如下信息：

kernel: raid5: Disk failure on sdb, disabling device.  
kernel: md0: resyncing spare disk sde to replace failed disk

检查 /proc/mdstat，如果配置的冗余磁盘可用，阵列可能已经开始重建。  
  
首先我们使用 mdadm --detail /dev/md0命令来查看一下RAID的状态：

\[root@localhost eric4ever\]\# mdadm --detail /dev/md0  
/dev/md0:  
Version : 00.90.00  
Creation Time : Thu May 24 13:45:35 2007  
Raid Level : raid5  
Array Size : 16777088 (16.00 GiB 17.18 GB)  
Used Dev Size : 8388544 (8.00 GiB 8.59 GB)  
Raid Devices : 3  
Total Devices : 5  
Preferred Minor : 0  
Persistence : Superblock is persistent  
  
Update Time : Thu May 24 14:07:55 2007  
State : active, degraded, recovering  
Active Devices : 2  
Working Devices : 3  
Failed Devices : 2  
Spare Devices : 1  
  
Layout : left-symmetric  
Chunk Size : 64K  
  
Rebuild Status : 3% complete  
  
UUID : 4b15050e:7d0c477d:98ed7d00:0f3c29e4  
Events : 0.6  
  
Number Major Minor RaidDevice State  
0 8 16 0 faulty spare /dev/sdb  
1 8 32 1 active sync /dev/sdc  
2 8 48 2 active sync /dev/sdd  
  
3 8 64 3 spare rebuilding /dev/sde

查看 /proc/mdstat：

\[root@localhost eric4ever\]\# cat /proc/mdstat 
Personalities : \[raid5\] 
read\_ahead 1024 sectors 
md0 : active raid5 sdb\[4\] sde\[3\] sdd\[2\] sdc\[1\] 
16777088 blocks level 5, 64k chunk, algorithm 2 \[3/2\] \[\_UU\] 
\[==>..................\] recovery = 10.2% (858824/8388544) finish=12.4min speed=10076K/sec 
unused devices: <none>

再查看一下RAID状态：

\[root@localhost eric4ever\]\# mdadm --detail /dev/md0  
/dev/md0:  
Version : 00.90.00  
Creation Time : Thu May 24 13:45:35 2007  
Raid Level : raid5  
Array Size : 16777088 (16.00 GiB 17.18 GB)  
Used Dev Size : 8388544 (8.00 GiB 8.59 GB)  
Raid Devices : 3  
Total Devices : 5  
Preferred Minor : 0  
Persistence : Superblock is persistent  
  
Update Time : Thu May 24 14:08:27 2007  
State : active, degraded, recovering  
Active Devices : 2  
Working Devices : 4  
Failed Devices : 1  
Spare Devices : 2  
  
Layout : left-symmetric  
Chunk Size : 64K  
  
Rebuild Status : 11% complete  
  
UUID : 4b15050e:7d0c477d:98ed7d00:0f3c29e4  
Events : 0.8  
  
Number Major Minor RaidDevice State  
0 0 0 0 removed  
1 8 32 1 active sync /dev/sdc  
2 8 48 2 active sync /dev/sdd  
  
3 8 64 3 spare /dev/sde  
4 8 16 4 spare /dev/sdb

已经完成到 11%了。查看一下日志消息：

\[root@localhost eric4ever\]\# tail /var/log/messages  
May 24 14:08:27 localhost kernel: --- rd:3 wd:2 fd:1  
May 24 14:08:27 localhost kernel: disk 0, s:0, o:0, n:0 rd:0 us:0 dev:\[dev 00:00\]  
May 24 14:08:27 localhost kernel: disk 1, s:0, o:1, n:1 rd:1 us:1 dev:sdc  
May 24 14:08:27 localhost kernel: disk 2, s:0, o:1, n:2 rd:2 us:1 dev:sdd  
May 24 14:08:27 localhost kernel: RAID5 conf printout:  
May 24 14:08:27 localhost kernel: --- rd:3 wd:2 fd:1  
May 24 14:08:27 localhost kernel: disk 0, s:0, o:0, n:0 rd:0 us:0 dev:\[dev 00:00\]  
May 24 14:08:27 localhost kernel: disk 1, s:0, o:1, n:1 rd:1 us:1 dev:sdc  
May 24 14:08:27 localhost kernel: disk 2, s:0, o:1, n:2 rd:2 us:1 dev:sdd  
May 24 14:08:27 localhost kernel: md: cannot remove active disk sde from md0 ...

使用 mdadm -E命令查看一下 /dev/sdb的情况：

\[root@localhost eric4ever\]\# mdadm -E /dev/sdb  
/dev/sdb:  
Magic : a92b4efc  
Version : 00.90.00  
UUID : 4b15050e:7d0c477d:98ed7d00:0f3c29e4  
Creation Time : Thu May 24 13:45:35 2007  
Raid Level : raid5  
Used Dev Size : 8388544 (8.00 GiB 8.59 GB)  
Array Size : 16777088 (16.00 GiB 17.18 GB)  
Raid Devices : 3  
Total Devices : 5  
Preferred Minor : 0  
  
Update Time : Thu May 24 14:08:27 2007  
State : active  
Active Devices : 2  
Working Devices : 4  
Failed Devices : 1  
Spare Devices : 2  
Checksum : a6a19662 - correct  
Events : 0.8  
  
Layout : left-symmetric  
Chunk Size : 64K  
  
Number Major Minor RaidDevice State  
this 4 8 16 4 spare /dev/sdb  
  
0 0 0 0 0 faulty removed  
1 1 8 32 1 active sync /dev/sdc  
2 2 8 48 2 active sync /dev/sdd  
3 3 8 64 3 spare /dev/sde  
4 4 8 16 4 spare /dev/sdb

自动修复完成后，我们再查看一下RAID的状态：

\[root@localhost eric4ever\]\# mdadm --detail /dev/md0 
/dev/md0: 
Version : 00.90.00 
Creation Time : Thu May 24 13:45:35 2007 
Raid Level : raid5 
Array Size : 16777088 (16.00 GiB 17.18 GB) 
Used Dev Size : 8388544 (8.00 GiB 8.59 GB) 
Raid Devices : 3 
Total Devices : 5 
Preferred Minor : 0 
Persistence : Superblock is persistent 
 
Update Time : Thu May 24 14:21:54 2007 
State : active 
Active Devices : 3 
Working Devices : 4 
Failed Devices : 1 
Spare Devices : 1 
 
Layout : left-symmetric 
Chunk Size : 64K 
 
UUID : 4b15050e:7d0c477d:98ed7d00:0f3c29e4 
Events : 0.9 
 
Number Major Minor RaidDevice State 
0 8 64 0 active sync /dev/sde 
1 8 32 1 active sync /dev/sdc 
2 8 48 2 active sync /dev/sdd 
 
4 8 16 4 spare /dev/sdb 
\[root@localhost eric4ever\]\# cat /proc/mdstat 
Personalities : \[raid5\] 
read\_ahead 1024 sectors 
md0 : active raid5 sdb\[4\] sde\[0\] sdd\[2\] sdc\[1\] 
16777088 blocks level 5, 64k chunk, algorithm 2 \[3/3\] \[UUU\] 
 
unused devices: <none>

我们可以看到 /dev/sde已经替换了 /dev/sdb。看看系统的日志消息：

\[root@localhost eric4ever\]\# tail /var/log/messages 
May 24 14:21:54 localhost kernel: --- rd:3 wd:3 fd:0 
May 24 14:21:54 localhost kernel: disk 0, s:0, o:1, n:0 rd:0 us:1 dev:sde 
May 24 14:21:54 localhost kernel: disk 1, s:0, o:1, n:1 rd:1 us:1 dev:sdc 
May 24 14:21:54 localhost kernel: disk 2, s:0, o:1, n:2 rd:2 us:1 dev:sdd 
May 24 14:21:54 localhost kernel: md: updating md0 RAID superblock on device 
May 24 14:21:54 localhost kernel: md: sdb \[events: 00000009\]<6>(write) sdb's sb offset: 8388544 
May 24 14:21:54 localhost kernel: md: sde \[events: 00000009\]<6>(write) sde's sb offset: 8388544 
May 24 14:21:54 localhost kernel: md: sdd \[events: 00000009\]<6>(write) sdd's sb offset: 8388544 
May 24 14:21:54 localhost kernel: md: sdc \[events: 00000009\]<6>(write) sdc's sb offset: 8388544 
May 24 14:21:54 localhost kernel: md: recovery thread got woken up ...

recovery thread got woken up ...  
  
这时我们可以从 /dev/md0中移除 /dev/sdb设备：

\[root@localhost eric4ever\]\# mdadm /dev/md0 -r /dev/sdb  
mdadm: hot removed /dev/sdb

类似地，我们可以使用下列命令向 /dev/md0中添加一个设备：

\[root@localhost eric4ever\]\# mdadm /dev/md0 --add /dev/sdf

**★监控RAID**

mdadm的监控模式提供一些实用的功能，你可以使用下列命令来监控 /dev/md0，delay参数意味着检测的时间间隔，这样紧急事件和严重的错误会及时发送给系统管理员：

\[root@localhost eric4ever\]\# mdadm --monitor --mail=eric4ever@localhost --delay=300 /dev/md0

当使用监控模式时，mdadm不会退出，你可以使用下列命令：

\[root@localhost eric4ever\]\# nohup mdadm --monitor --mail=eric4ever@localhost --delay=300 /dev/md0 &  
\[1\] 3113  
\[root@localhost eric4ever\]\# nohup: appending output to \`nohup.out'

[raidtools_Linux Soft RAID]: http://www3.eastgame.net/read.php?tid=1148250&u=573060
[en]: http://eric4ever.googlepages.com/raidcalc_en.htm
[ch]: http://eric4ever.googlepages.com/raidcalc_ch.htm
[en 1]: http://eric4ever.googlepages.com/comparison_en.htm
[ch 1]: http://eric4ever.googlepages.com/comparison_ch.htm
[my googlepage]: http://eric4ever.googlepages.com/
[Neil Brown]: http://www.cse.unsw.edu.au/~neilb/source/mdadm/
[LATEST.tgz]: http://www.cse.unsw.edu.au/~neilb/source/mdadm/LATEST.tgz
[mdadm-2.6.2.tgz]: http://www.cse.unsw.edu.au/~neilb/source/mdadm/mdadm-2.6.2.tgz
[Link 1]: http://www.cse.unsw.edu.au/~neilb/source/mdadm/RPM
[4]: http://www3.eastgame.net/read.php?tid=1148677&u=573060&pn=4#10084914