一、操作过程
1.df -h查看分区大小情况;
```
[root@localhost /]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root
50G 1.9G 45G 5% /
tmpfs 7.5G 0 7.5G 0% /dev/shm
/dev/sda1 477M 90M 362M 20% /boot
/dev/mapper/VolGroup-lv_home
860G 101M 816G 1% /home
tmpfs 4.0G 0 4.0G 0% /var/spool/MailScanner/incoming
```
2.卸载home分区
```
[root@localhost /]# umount /home
```
3.查看卸载情况
```
[root@localhost /]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root
50G 1.9G 45G 5% /
tmpfs 7.5G 0 7.5G 0% /dev/shm
/dev/sda1 477M 90M 362M 20% /boot
tmpfs 4.0G 0 4.0G 0% /var/spool/MailScanner/incoming
```
4.重新整合home分区
```
[root@localhost /]# e2fsck -f /dev/mapper/VolGroup-lv_home
e2fsck 1.41.12 (17-May-2010)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/mapper/VolGroup-lv_home: 50/57212928 files (10.0% non-contiguous), 3649291/228843520 blocks
```
5.从新设定home分区的大小：
```
[root@localhost /]# resize2fs -p /dev/mapper/VolGroup-lv_home 50G
resize2fs 1.41.12 (17-May-2010)
Resizing the filesystem on /dev/mapper/VolGroup-lv_home to 13107200 (4k) blocks.
Begin pass 2 (max = 32849)
Relocating blocks XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Begin pass 3 (max = 6984)
Scanning inode table XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Begin pass 4 (max = 17)
Updating inode references XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
The filesystem on /dev/mapper/VolGroup-lv_home is now 13107200 blocks long.
```
6.重新挂载home分区
```
[root@localhost /]# mount /home
```
7.查看挂载情况
```
[root@localhost /]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root
50G 1.9G 45G 5% /
tmpfs 7.5G 0 7.5G 0% /dev/shm
/dev/sda1 477M 90M 362M 20% /boot
tmpfs 4.0G 0 4.0G 0% /var/spool/MailScanner/incoming
/dev/mapper/VolGroup-lv_home
50G 81M 47G 1% /home
```
8.将lv_home逻辑分区减小到指定大小
```
[root@localhost /]# lvreduce -L 50G /dev/mapper/VolGroup-lv_home
Rounding size to boundary between physical extents: 52.00 MiB.
WARNING: Reducing active and open logical volume to 52.00 MiB.
THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce VolGroup/lv_home? [y/n]: y
Size of logical volume VolGroup/lv_home changed from 872.97 GiB (223480 extents) to 52.00 MiB (13 extents).
Logical volume lv_home successfully resized.
```
9.查询卷组的信息：
```
[root@localhost /]# vgdisplay
--- Volume group ---
VG Name VolGroup
System ID
Format lvm2
Metadata Areas 1
Metadata Sequence No 6
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 930.51 GiB
PE Size 4.00 MiB
Total PE 238210
Alloc PE / Size 14743 / 57.59 GiB
Free PE / Size 223467 / 872.92 GiB #Free PE / Size指定的应该是现在可在分配的空间
VG UUID Acapyj-Dw5o-Hi3c-RLVe-AmHl-AD83-Nek4Qv
```
10.增加root分区的大小
```
[root@localhost /]# lvextend -L +870G /dev/mapper/VolGroup-lv_root
```
11.从新设定root分区的大小：
```
[root@localhost /]# resize2fs -p /dev/mapper/VolGroup-lv_root
resize2fs 1.41.12 (17-May-2010)
Filesystem at /dev/mapper/VolGroup-lv_root is mounted on /; on-line resizing required
old desc_blocks = 4, new_desc_blocks = 58
Performing an on-line resize of /dev/mapper/VolGroup-lv_root to 241696768 (4k) blocks.
The filesystem on /dev/mapper/VolGroup-lv_root is now 241696768 blocks long.
```
12.重新查看分区大小
```
[root@localhost /]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root
908G 1.9G 860G 1% /
tmpfs 7.5G 0 7.5G 0% /dev/shm
/dev/sda1 477M 90M 362M 20% /boot
tmpfs 4.0G 0 4.0G 0% /var/spool/MailScanner/incoming
/dev/mapper/VolGroup-lv_home
50G 81M 47G 1% /home
```
二、遇到问题解决办法
1、在卸载/home目录的时候失败
可先执行如下fuser命令，然后再umount即可：
```
[root@CentOS-78 /]# fuser -m /home
```
2、设定完lv_home的大小，再次mount该分区时，发现用df命令无法看到给分区，此时只要在mount一次即可
3、在设定lv_root的大小时，不要把Free PE / Size的空间全部都用上，这很可能会出现Free PE空间不足的现象，建议保留一点Free PE的空间。