磁盘管理——RAID 0

一什么是RAID0

RAID0，将数据分为几半，写到多个磁盘 A ：A1 A2…… 性能提升。最小需要两个磁盘。

将多个磁碟合并成一个大的磁碟，不具有冗余，并行I/O，速度最快。RAID 0亦称为带区集。它是将多个磁盘并列起来，成为一个大磁盘。在存放数据时，其将数据按磁盘的个数来进行分段，然后同时将这些数据写进这些盘中，所以在所有的级别中，RAID 0的速度是最快的。但是RAID 0没有冗余功能，如果一个磁盘（物理）损坏，则所有的数据都会丢失，危险程度与JBOD相当。

理论上越多的磁碟效能就等于“单一磁碟效能”×“磁碟数”，但实际上受限于汇流排I/O瓶颈及其它因素的影响，RAID效能会随边际递减，也就是说，假设一个磁碟的效能是50MB每秒，两个磁碟的RAID 0效能约96MB每秒，三个磁碟的RAID 0也许是130MB每秒而不是150MB每秒，所以两个磁碟的RAID 0最能明显感受到效能的提升。

但如果是以软体方式来实作RAID，则磁碟的空间则不见得受限于此（例如Linux Software RAID），透过软体实作可以经由不同的组合而善用所有的磁碟空间。

二 RAID0演示

第一步对磁盘进行分区

[root@serv01 /]# ls /dev/sdb
/dev/sdb
[root@serv01 /]# ls /dev/sdc
/dev/sdc[root@serv01 /]# ls /dev/sdb* /dev/sdc* -l
brw-rw----. 1 root disk 8, 16 Jul 31 23:20/dev/sdb
brw-rw----. 1 root disk 8, 17 Jul 31 23:20/dev/sdb1
brw-rw----. 1 root disk 8, 32 Jul 31 23:21/dev/sdc
brw-rw----. 1 root disk 8, 33 Jul 31 23:21/dev/sdc1
#分区：只分一个区（/dev/sdb），注意需要把分区类型改为fd(t,fd)
#Linux raid autodetect：fd
[root@serv01 /]# fdisk /dev/sdb
#分区：只分一个区（/dev/sdc），注意需要把分区类型改为fd(t,fd)
[root@serv01 /]# fdisk /dev/sdc
[root@serv01 /]# fdisk -l | grep -e sdb -esdc
Disk /dev/sdb: 2147 MB, 2147483648 bytes
/dev/sdb1               1         261    2096451   fd  Linux raid autodetect
Disk /dev/sdc: 2147 MB, 2147483648 bytes
/dev/sdc1               1         261    2096451   fd  Linux raid autodetect
#安装mdadm——软RAID的实现
[root@serv01 /]# yum install /sbin/mdadm -y[root@serv01 /]# ls /dev/sdb*
/dev/sdb /dev/sdb1
[root@serv01 /]# ls /dev/sdc*
/dev/sdc /dev/sdc1#创建RAID
[root@serv01 /]# mdadm --create /dev/md0--level 0 --raid-devices=2 /dev/sdb1 /dev/sdc1
mdadm: /dev/sdb1 appears to contain anext2fs file systemsize=208812K  mtime=Wed Jul 3122:17:43 2013
mdadm: /dev/sdb1 appears to be part of araid array:level=raid0 devices=0 ctime=Thu Jan 1 07:00:00 1970
mdadm: partition table exists on /dev/sdb1but will be lost ormeaningless after creating array
Continue creating array? y
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
[root@serv01 /]# ls /dev/md0
/dev/md0#查看/dev/md0的详细信息
[root@serv01 /]# mdadm --detail /dev/md0
/dev/md0:Version : 1.2Creation Time : Wed Jul 31 23:30:26 2013Raid Level : raid0Array Size : 4190208 (4.00 GiB 4.29 GB)Raid Devices : 2Total Devices : 2Persistence : Superblock is persistentUpdate Time : Wed Jul 31 23:30:26 2013State : cleanActive Devices : 2
Working Devices : 2Failed Devices : 0Spare Devices : 0Chunk Size : 512KName : serv01.host.com:0  (localto host serv01.host.com)UUID : 1f1a007f:7ed82aa0:49722d2f:1e664330Events : 0Number   Major   Minor  RaidDevice State0       8       17       0      active sync   /dev/sdb11       8       33       1      active sync   /dev/sdc1[root@serv01 /]# cat /proc/mdstat
Personalities : [raid0]
md0 : active raid0 sdc1[1] sdb1[0]4190208 blocks super 1.2 512k chunksunused devices: <none>

第二步格式化

[root@serv01 /]# mkfs.ext4 /dev/md0
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=128 blocks, Stripe width=256 blocks
262144 inodes, 1047552 blocks
52377 blocks (5.00%) reserved for the superuser
First data block=0
Maximum filesystem blocks=1073741824
32 block groups
32768 blocks per group, 32768 fragments pergroup
8192 inodes per group
Superblock backups stored on blocks:32768,98304, 163840, 229376, 294912, 819200, 884736Writing inode tables: done
Creating journal (16384 blocks): mdone
Writing superblocks and filesystemaccounting information: doneThis filesystem will be automaticallychecked every 26 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.
[root@serv01 /]# mount /dev/md0 /web/
[root@serv01 /]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2             9.7G  1.1G 8.1G  12% /
tmpfs                 188M     0 188M   0% /dev/shm
/dev/sda1             194M   25M 160M  14% /boot
/dev/sda5             4.0G  137M 3.7G   4% /opt
/dev/sr0              3.4G  3.4G    0 100% /iso
/dev/md0              4.0G   72M 3.7G   2% /web[root@serv01 /]# vim /etc/fstab
[root@serv01 /]# echo "/dev/md0 /webext4 defaults 1 2" >> /etc/fstab
[root@serv01 /]# cat /etc/fstab#
# /etc/fstab
# Created by anaconda on Tue Jul 2300:54:37 2013
#
# Accessible filesystems, by reference, aremaintained under '/dev/disk'
# See man pages fstab(5), findfs(8),mount(8) and/or blkid(8) for more info
#
UUID=110fab7c-85c4-4bae-9114-98bc2ada24d8/                       ext4    defaults        1 1
UUID=ab434325-bf02-48e9-8ce7-78494a8ac71e/boot                   ext4    defaults        1 2
UUID=02ed2b3b-b7e1-493d-9a43-8e1dcac8aa6f/opt                    ext4    defaults        1 2
UUID=a088a35a-16d8-456a-a177-95c769c16e41swap                    swap    defaults        0 0
tmpfs                   /dev/shm                tmpfs   defaults        0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc   defaults        0 0
/dev/md0 /web ext4 defaults 1 2

第三步重启后更名的解决及演示RAID0的应用

#然后重启，发现错误
#查看，发现已经更名[root@serv01 ~]# ls /dev/md
md/   md127
[root@serv01 ~]# mdadm --manage /dev/md127--stop
mdadm: stopped /dev/md127
[root@serv01 ~]# ls /dev/md
md-device-map
[root@serv01 ~]# mdadm --datail /dev/md0
mdadm: unrecognized option '--datail'
Usage: mdadm --helpforhelp
#查看RAID状态，发现没有使用
[root@serv01 ~]# cat /proc/mdstat
Personalities : [raid0]
unused devices: <none>
#固定名字，然后启动RAID
[root@serv01 ~]# mdadm --assemble /dev/md0/dev/sdb1 /dev/sdc1
mdadm: /dev/md0 has been started with 2drives.
#查看状态，已经启动了
[root@serv01 ~]# cat /proc/mdstat
Personalities : [raid0]
md0 : active raid0 sdb1[0] sdc1[1]4190208 blocks super 1.2 512k chunksunused devices: <none>
#将RAID的信息保存到配置文件
[root@serv01 ~]# mdadm --detail —scan >/etc/mdadm.conf
#然后输入设备的挂载信息
[root@serv01 ~]# echo "/dev/md0 /webext4 defaults 1 2" >> /etc/fstab
#然后重启
[root@serv01 ~]# reboot[root@larrywen 0731]# ssh 192.168.1.11
root@192.168.1.11's password:
Last login: Wed Jul 31 23:43:44 2013 from192.168.1.1
[root@serv01 ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2             9.7G  1.1G 8.1G  12% /
tmpfs                 188M     0 188M   0% /dev/shm
/dev/sda1             194M  25M  160M  14% /boot
/dev/sda5             4.0G  137M 3.7G   4% /opt
/dev/md0              4.0G   72M 3.7G   2% /web
/dev/sr0              3.4G  3.4G    0 100% /iso
[root@serv01 ~]# cat /proc/mdstat
Personalities : [raid0]
md0 : active raid0 sdb1[0] sdc1[1]4190208 blocks super 1.2 512k chunksunused devices: <none>
#发现正常
[root@serv01 ~]# ls /dev/md
md/ md0#磁盘大小不一样，按照小的，比如一个磁盘是1G，另一个是2G，那么真正有用的只有1G#RAID0：一块坏了，另一块就无法使用
[root@serv01 ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2             9.7G  1.1G 8.1G  12% /
tmpfs                 188M     0 188M   0% /dev/shm
/dev/sda1             194M   25M 160M  14% /boot
/dev/sda5             4.0G  137M 3.7G   4% /opt
/dev/md0              4.0G   72M 3.7G   2% /web
/dev/sr0              3.4G  3.4G    0 100% /iso
[root@serv01 ~]# fdisk /dev/sdbWARNING: DOS-compatible mode is deprecated.It's strongly recommended toswitch off the mode (command 'c') and change display units tosectors (command 'u').Command (m for help): pDisk /dev/sdb: 2147 MB, 2147483648 bytes
255 heads, 63 sectors/track, 261 cylinders
Units = cylinders of 16065 * 512 = 8225280bytes
Sector size (logical/physical): 512 bytes /512 bytes
I/O size (minimum/optimal): 512 bytes / 512bytes
Disk identifier: 0xf85ef5bdDevice Boot      Start         End      Blocks  Id  System
/dev/sdb1               1         261    2096451   fd  Linux raid autodetectCommand (m for help): o
Building a new DOS disklabel with diskidentifier 0xc29e300a.
Changes will remain in memory only, untilyou decide to write them.
After that, of course, the previous contentwon't be recoverable.Warning: invalid flag 0x0000 of partitiontable 4 will be corrected by w(rite)WARNING: DOS-compatible mode is deprecated.It's strongly recommended toswitch off the mode (command 'c') and change display units tosectors (command 'u').Command (m for help): w
The partition table has been altered!Calling ioctl() to re-read partition table.WARNING: Re-reading the partition tablefailed with error 16: Device or resource busy.
The kernel still uses the old table. Thenew table will be used at
the next reboot or after you runpartprobe(8) or kpartx(8)
Syncing disks.
[root@serv01 ~]# fdisk -l|/dev/sdb1
-bash: /dev/sdb1: Permission denied
Disk /dev/sdd doesn't contain a validpartition table
Disk /dev/sde doesn't contain a validpartition table
Disk /dev/sdf doesn't contain a validpartition table
Disk /dev/sdg doesn't contain a validpartition table
Disk /dev/md0 doesn't contain a validpartition table
[root@serv01 ~]# fdisk -l|/dev/sdb
-bash: /dev/sdb: Permission denied
Disk /dev/sdd doesn't contain a validpartition table
Disk /dev/sde doesn't contain a validpartition table
Disk /dev/sdf doesn't contain a validpartition table
Disk /dev/sdg doesn't contain a validpartition table
Disk /dev/md0 doesn't contain a validpartition table
#重启发现提示你是否进入修复模式
#重新挂载根分区
mount -o remount,rw /
#删除配置的RAID，然后重启
#重新查看，然后发现RAID已经不能使用了
[root@larrywen 0731]# ssh 192.168.1.11
root@192.168.1.11's password:
Last login: Wed Jul 31 23:49:41 2013 from192.168.1.1
[root@serv01 ~]# cat /proc/mdstat
Personalities : [raid0]
md0 : inactive sdc1[1]2095104 blocks super 1.2unused devices: <none>
[root@serv01 ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2             9.7G  1.1G 8.1G  12% /
tmpfs                 188M     0 188M   0% /dev/shm
/dev/sda1             194M   25M 160M  14% /boot
/dev/sda5             4.0G  137M 3.7G   4% /opt
/dev/sr0              3.4G  3.4G    0 100% /iso
[root@serv01 ~]# mdadm --detail /dev/md
md/ md0
[root@serv01 ~]# mdadm --detail /dev/md0
/dev/md0:Version : 1.2Creation Time : Wed Jul 31 23:30:26 2013Raid Level : raid0Raid Devices : 2Total Devices : 1Persistence : Superblock is persistentUpdate Time : Wed Jul 31 23:30:26 2013State : active, FAILED, Not StartedActive Devices : 1
Working Devices : 1Failed Devices : 0Spare Devices : 0Chunk Size : 512KName : serv01.host.com:0  (localto host serv01.host.com)UUID : 1f1a007f:7ed82aa0:49722d2f:1e664330Events : 0Number   Major   Minor  RaidDevice State0       0        0       0      removed1       8       33       1      active sync   /dev/sdc1

第四步实验完毕，清理磁盘

#清理数据，做RAID必须做如下操作
#首先停掉RAID
[root@serv01 ~]# mdadm --manage /dev/md0--stop
mdadm: stopped /dev/md0
[root@serv01 ~]# rm -rf /etc/mdadm.conf
[root@serv01 ~]# mdadm -E /dev/sdb1
mdadm: cannot open /dev/sdb1: No such fileor directory
#检测发现有残留信息
[root@serv01 ~]# mdadm -E /dev/sdc1
/dev/sdc1:Magic : a92b4efcVersion : 1.2Feature Map : 0x0Array UUID : 1f1a007f:7ed82aa0:49722d2f:1e664330Name : serv01.host.com:0  (localto host serv01.host.com)Creation Time : Wed Jul 31 23:30:26 2013Raid Level : raid0Raid Devices : 2Avail Dev Size : 4190854 (2046.66 MiB 2145.72MB)Data Offset : 2048 sectorsSuper Offset : 8 sectorsState : cleanDevice UUID : 7e3d4caf:35001960:b95d9eae:19fa3093Update Time : Wed Jul 31 23:30:26 2013Checksum : 64b18466 - correctEvents : 0Chunk Size : 512KDevice Role : Active device 1Array State : AA ('A' == active, '.' == missing)
#清空磁盘
[root@serv01 ~]# mdadm --misc—zero-superblock /dev/sdc1
[root@serv01 ~]# fdisk /dev/sdbWARNING: DOS-compatible mode is deprecated.It's strongly recommended toswitch off the mode (command 'c') andchange display units tosectors (command 'u').Command (m for help): n
Command actione   extendedp   primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-261, default 1):
Using default value 1
Last cylinder, +cylinders or +size{K,M,G}(1-261, default 261):
Using default value 261Command (m for help): w
The partition table has been altered!Calling ioctl() to re-read partition table.
Syncing disks.
[root@serv01 ~]# mdadm -E /dev/sdb1
/dev/sdb1:Magic : a92b4efcVersion : 1.2Feature Map : 0x0Array UUID : 1f1a007f:7ed82aa0:49722d2f:1e664330Name : serv01.host.com:0  (localto host serv01.host.com)Creation Time : Wed Jul 31 23:30:26 2013Raid Level : raid0Raid Devices : 2Avail Dev Size : 4190854 (2046.66 MiB 2145.72MB)Data Offset : 2048 sectorsSuper Offset : 8 sectorsState : cleanDevice UUID : f76937d2:74ac3af1:506bed88:795c81edUpdate Time : Wed Jul 31 23:30:26 2013Checksum : 4d5dcd15 - correctEvents : 0Chunk Size : 512KDevice Role : Active device 0Array State : AA ('A' == active, '.' == missing)
#清空磁盘
[root@serv01 ~]# mdadm --misc--zero-superblock /dev/sdb1
mdadm: Couldn't open /dev/sdb1 for write -not zeroing
[root@serv01 ~]# cat /proc/mdstat
Personalities : [raid0]
md0 : inactive sdb1[0](S)2095427 blocks super 1.2unused devices: <none>
root@serv01 ~]# mdadm --manage /dev/md0--stop
mdadm: stopped /dev/md0
[root@serv01 ~]# mdadm --misc--zero-superblock /dev/sdb1
[root@serv01 ~]#
[root@serv01 ~]# mdadm -E /dev/sdb1
/dev/sdb1:MBR Magic : aa55
[root@serv01 ~]# mdadm -E /dev/sdc1
mdadm: No md superblock detected on/dev/sdc1.

三参考资料

http://zh.wikipedia.org/wiki/RAID

四相关文章

磁盘管理——RAID 1
磁盘管理——RAID 10
磁盘管理——RAID 5
磁盘管理——RAID 6
磁盘管理——LVM
磁盘管理——小实验

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