centos 扩展root根分区的大小

目标：将VolGroup-lv_home缩小到125G，并将剩余的空间添加给VolGroup-lv_root
 
1.首先查看磁盘使用情况
[root@localhost ~]# df -h
文件系统    容量  已用 可用  已用% 挂载点    
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg_hostname-lv_root
                       20G  8.7G  9.6G  48% /
tmpfs                 6.9G   72K  6.9G   1% /dev/shm
/dev/sda1             485M   38M  422M   9% /boot
/dev/mapper/vg_hostname-lv_home
                      171G  110G   53G  68% /home
/dev/sdb5             2.0T  805G  1.1T  43% /xxxx_sdb5
/dev/sdc5             1.7T  197M  1.6T   1% /xxxx_sdc5

2、卸载/home
[root@localhost ~]# umount /home
umount: /home: device is busy.
        (In some cases useful info about processes that use
         the device is found by lsof(8) or fuser(1))

umount /home 如果提示无法卸载，则是有进程占用/home，使用如下命令来终止占用进程：
[root@localhost ~]# fuser -m /home  
/home:               31112m
top
kill -9 31112
 
3、调整分区大小
[root@localhost ~]# resize2fs -p /dev/mapper/vg_hostname-lv_home 125G
resize2fs 1.41.12 (17-May-2010)
Please run 'e2fsck -f /dev/mapper/vg_hostname-lv_home' first.

如果提示运行“e2fsck -f /dev/mapper/VolGroup-lv_home”，则执行相关命令：
[root@localhost ~]# e2fsck -f /dev/mapper/vg_hostname-lv_home 然后重新执行命令：
[root@localhost ~]# resize2fs -p /dev/mapper/vg_hostname-lv_home 125G
resize2fs 1.41.12 (17-May-2010)
Resizing the filesystem on /dev/mapper/vg_hostname-lv_home to 32768000 (4k) blocks.
Begin pass 2 (max = 7110485)
Relocating blocks             XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Begin pass 3 (max = 1385)
Scanning inode table          XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Begin pass 4 (max = 3237)
Updating inode references     XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
The filesystem on /dev/mapper/vg_hostname-lv_home is now 32768000 blocks long.

注：resize2fs 为重新设定磁盘大小，只是重新指定一下大小，并不对结果有影响，需要下面lvreduce的配合
 
4、挂载上/home，查看磁盘使用情况
[root@localhost ~]# mount /home
[root@localhost ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg_hostname-lv_root
                       20G  8.7G  9.6G  48% /
tmpfs                 6.9G   72K  6.9G   1% /dev/shm
/dev/sda1             485M   38M  422M   9% /boot
/dev/sdb5             2.0T  805G  1.1T  43% /xxxx_sdb5
/dev/sdc5             1.7T  197M  1.6T   1% /xxxx_sdc5
/dev/mapper/vg_hostname-lv_home
                      124G  110G  7.4G  94% /home

5、设置空闲空间
使用lvreduce指令用于减少LVM逻辑卷占用的空间大小。可能会删除逻辑卷上已有的数据，所以在操作前必须进行确认。记得输入 “y”
[root@localhost ~]# lvreduce -L 125G /dev/mapper/vg_hostname-lv_home
  WARNING: Reducing active and open logical volume to 125.00 GiB
  THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce lv_home? [y/n]: y
  Reducing logical volume lv_home to 125.00 GiB
  Logical volume lv_home successfully resized

注：lvreduce -L 125G的意思为设置当前文件系统为125G，如果lvreduce -l 125G是指从当前文件系统上减少125G
使用lvreduce减小逻辑卷的大小。注意：减小后的大小不能小于文件的大小，否则会丢失数据。
 
可以使用vgdisplay命令等查看一下可以操作的大小。也可以是用fdisk -l命令查看详细信息。
[root@localhost ~]# vgdisplay
  --- Volume group ---
  VG Name               vg_hostname
  System ID             
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  5
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                3
  Open LV               3
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               199.51 GiB
  PE Size               4.00 MiB
  Total PE              51074
  Alloc PE / Size       38758 / 151.40 GiB
  Free  PE / Size       12316 / 48.11 GiB
  VG UUID               zk1eHH-QXe8-sdm8-cKfF-StSl-yffz-Dfe9sF
注：vgdisplay为显示LVM卷组的元数据信息
 
6.把闲置空间挂在到根目录下
[root@localhost ~]# lvextend -L +48G /dev/mapper/vg_hostname-lv_root
  Extending logical volume lv_root to 67.53 GiB
  Logical volume lv_root successfully resized
注：lvextend -L +48G为在文件系统上增加48G
[root@localhost ~]# resize2fs -p /dev/mapper/vg_hostname-lv_root
resize2fs 1.41.12 (17-May-2010)
Filesystem at /dev/mapper/vg_hostname-lv_root is mounted on /; on-line resizing required
old desc_blocks = 2, new_desc_blocks = 5
Performing an on-line resize of /dev/mapper/vg_hostname-lv_root to 17702912 (4k) blocks.
The filesystem on /dev/mapper/vg_hostname-lv_root is now 17702912 blocks long.

7、检查调整结果
[root@localhost ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg_hostname-lv_root
                       67G  8.7G   55G  14% /
tmpfs                 6.9G   72K  6.9G   1% /dev/shm
/dev/sda1             485M   38M  422M   9% /boot
/dev/sdb5             2.0T  805G  1.1T  43% /xxxx_sdb5
/dev/sdc5             1.7T  197M  1.6T   1% /xxxx_sdc5
/dev/mapper/vg_hostname-lv_home
                      124G  110G  7.4G  94% /home