LVM逻辑卷实现磁盘镜像

LVM逻辑卷实现磁盘镜像

大家都知道用lvm作分区扩展很方便，其实用lvs还可以用作磁盘镜像，类似于raid1，即多块磁盘互相同步备份，可以有效避免数据丢失的尴尬。

1.新建磁盘分区

新建4个分区/dev/sdb1,/dev/sdb2,/dev/sdb3,/dev/sdb4，如：

Disk /dev/sdb: 1999.8 GB, 1999844147200 bytes
255 heads, 63 sectors/track, 243133 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1         374     3004123+  83  Linux
/dev/sdb2             375         748     3004155   83  Linux
/dev/sdb3             749        1122     3004155   83  Linux
/dev/sdb4            1123        1496     3004155   83  Linux

其中/dev/sdb1,/dev/sdb2用作数据磁盘，/dev/sdb2用作/dev/sdb1的镜像；
/dev/sdb3用作日志；/dev/sdb4作为备用，当sdb1或sdb2损害时备用，类似于raid5中的热备盘。

2.创建pv和vg

pvcreate /dev/sdb1

pvcreate /dev/sdb2
pvcreate /dev/sdb3
pvcreate /dev/sdb4
vgcreate vg_test  /dev/sdb1 /dev/sdb2 /dev/sdb3

注：/dev/sdb4暂未使用，待备用

3.创建包含镜像功能的逻辑卷(mirror_test)

[root@localhost ~]# lvcreate -L 2.8G -m1 -n mirror_test vg_test /dev/sdb1 /dev/sdb2 /dev/sdb3
  Rounding up size to full physical extent 2.80 GB
  Logical volume "mirror_test" created
[root@localhost ~]# lvs -a -o +devices
  LV                     VG                Attr   LSize   Origin Snap%  Move Log              Copy%  Convert Devices

  mirror_test            vg_test           mwi-a-   2.80G                    mirror_test_mlog  24.27         mirror_test_mimage_0(0),mirror_test_mimage_1(0)
  [mirror_test_mimage_0] vg_test           Iwi-ao   2.80G                                                    /dev/sdb1(0)
  [mirror_test_mimage_1] vg_test           Iwi-ao   2.80G                                                    /dev/sdb2(0)
  [mirror_test_mlog]     vg_test           lwi-ao   4.00M                                                    /dev/sdb3(0)

其中：-m1参数为创建镜像；-L参数为设定镜像卷的大小为2.8G；-n参数为指定镜像名称。这个镜像包括三部分：sdb1和sdb2位数据卷和镜像卷，sdb3为日志卷。

4.格式化挂载

[root@localhost ~]# mkfs.ext3 /dev/vg_test/mirror_test
[root@localhost ~]# mkdir -p /test
[root@localhost ~]# mount /dev/vg_test/mirror_test /test

5.测试

(1)创建测试文件

for x in {1..100};do echo "$x test test test " >> /test/test.txt ;done

(2)模拟对/dev/sdb2进行破坏

[root@localhost ~]# dd if=/dev/zero of=/dev/sdb2 count=10 bs=1M
10+0 records in
10+0 records out
10485760 bytes (10 MB) copied, 0.008574 seconds, 1.2 GB/s
[root@localhost ~]# lvs -a -o +devices
  Couldn't find device with uuid z74R0l-ZLUV-X6TS-QrpF-nXDZ-gc74-UvwGC0.
  LV                     VG                Attr   LSize   Origin Snap%  Move Log              Copy%  Convert Devices

  mirror_test            vg_test           mwi-ao   2.80G                    mirror_test_mlog 100.00         mirror_test_mimage_0(0),mirror_test_mimage_1(0)
  [mirror_test_mimage_0] vg_test           iwi-ao   2.80G                                                    /dev/sdb1(0)
  [mirror_test_mimage_1] vg_test           iwi-ao   2.80G                                                    unknown device(0)
  [mirror_test_mlog]     vg_test           lwi-ao   4.00M                                                    /dev/sdb3(0)

查看状态发现/dev/sdb2处于“unknown device(0)”状态。

[root@localhost ~]# lvscan
  Couldn't find device with uuid z74R0l-ZLUV-X6TS-QrpF-nXDZ-gc74-UvwGC0.
  ACTIVE            '/dev/vg_test/mirror_test' [2.80 GB] inherit

(3)重新挂载确认数据可读取

[root@localhost ~]# umount /test
[root@localhost test]# cd
[root@localhost ~]# mount /dev/vg_test/mirror_test /test
[root@localhost ~]# cat /test/test.txt
lvs mirror test

(4)将坏掉的设备删除

[root@localhost ~]# vgreduce --removemissing --force vg_test
  Couldn't find device with uuid z74R0l-ZLUV-X6TS-QrpF-nXDZ-gc74-UvwGC0.
  WARNING: Bad device removed from mirror volume, vg_test/mirror_test
  WARNING: Mirror volume, vg_test/mirror_test converted to linear due to device failure.
  Wrote out consistent volume group vg_test

移除后vgdisplay /dev/vg_test发现mirrored volumes选项没有了；并且由于sdb2的实效，
镜像mirror_test也已经有mirror模式转变成线性模式，如果恢复我们需要用到lvconvert命令来恢复。

(5)镜像数据恢复

[root@localhost ~]# vgextend vg_test /dev/sdb4  
  Volume group "vg_test" successfully extended  
[root@localhost ~]# lvconvert -m1 /dev/vg_test/mirror_test /dev/sdb1 /dev/sdb4 /dev/sdb3  
  vg_test/mirror_test: Converted: 0.0%  
  vg_test/mirror_test: Converted: 20.8%  
  vg_test/mirror_test: Converted: 40.4%  
  vg_test/mirror_test: Converted: 60.1%  
  vg_test/mirror_test: Converted: 79.4%  
  vg_test/mirror_test: Converted: 99.2%  
  vg_test/mirror_test: Converted: 100.0%  

ok，恢复完成，我们来查看下状态：

[root@localhost ~]# lvdisplay /dev/vg_test  
  --- Logical volume ---  
  LV Name                /dev/vg_test/mirror_test  
  VG Name                vg_test  
  LV UUID                RUamnD-nYCt-D9yp-cNdX-ix1y-r9P9-wenSjb  
  LV Write Access        read/write  
  LV Status              available  
  # open                 1  
  LV Size                2.80 GB  
  Current LE             717  
  Mirrored volumes       2  
  Segments               1  
  Allocation             inherit  
  Read ahead sectors     auto  
  - currently set to     256  
  Block device           253:8  
     
[root@localhost ~]# cat /test/test.txt   
lvs mirror test  
[root@localhost ~]# lvs -a -o +devices  
  LV                     VG                Attr   LSize   Origin Snap%  Move Log              Copy%  Convert Devices                                          
                                
  mirror_test            vg_test           mwi-ao   2.80G                    mirror_test_mlog 100.00         mirror_test_mimage_0(0),mirror_test_mimage_1(0)  
  [mirror_test_mimage_0] vg_test           iwi-ao   2.80G                                                    /dev/sdb1(0)                                     
  [mirror_test_mimage_1] vg_test           iwi-ao   2.80G                                                    /dev/sdb4(0)                                     
  [mirror_test_mlog]     vg_test           lwi-ao   4.00M                                                    /dev/sdb3(0)   

镜像卷由原来的sdb2转变为sdb4

总结：在某些不支持raid的服务器上，我们可以使用lvm的磁盘镜像来解决防止数据丢失的问题了。