情况:
  home:500G
  root:50G
  root分区不够用
  思路:把home分区的空间划一部分到root分区
  # 设置home分区大小为200G,释放300G空间
  $ lvreduce -L 200G /dev/centos/home
  # 将空闲空间扩展到root分区
  $ lvextend -l +FREE /dev/centos/root
  # 使用XFS文件系统自带的命令集增加分区空间
  $ xfs_growfs /dev/mapper/centos-root
  实例
  situation
  挂载在根目录的分区 /dev/mapper/centos-root 爆满,占用
$ df -h
Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/centos-root   50G   50G   19M /
devtmpfs                  32G     0   32G   0% /dev
tmpfs                     32G     0   32G   0% /dev/shm
tmpfs                     32G  2.5G   29G   8% /run
tmpfs                     32G     0   32G   0% /sys/fs/cgroup
/dev/mapper/centos-home  476G   33M  476G   1% /home
/dev/sda1                497M  238M  259M  48% /boot
tmpfs                    6.3G     0  6.3G   0% /run/user/0
analyze
  挂载在根目录的分区空间太小,只有50G,而服务器 home 目录为非常用目录,挂在了近500G的空间。
  思路:从 centos-home 分区划出300G空间到 centos-root 分区。
  operation
  1.查看各分区信息
$ lvdisplay
--- Logical volume ---
LV Path                /dev/centos/home
LV Name                home
VG Name                centos
LV UUID                1fAt1E-bQsa-1HXR-MCE2-5VZ1-xzBz-iI1SLv
LV Write Access        read/write
LV Creation host, time localhost, 2016-10-26 17:23:47 +0800
LV Status              available
# open                 0
LV Size                475.70 GiB
Current LE             121778
Segments               1
Allocation             inherit
Read ahead sectors     auto
- currently set to     256
Block device           253:2
--- Logical volume ---
LV Path                /dev/centos/root
LV Name                root
VG Name                centos
LV UUID                lD64zY-yc3Z-SZaB-dAjK-03YM-2gM8-pfj4oo
LV Write Access        read/write
LV Creation host, time localhost, 2016-10-26 17:23:48 +0800
LV Status              available
# open                 1
LV Size                50.00 GiB
Current LE             12800
Segments               1
Allocation             inherit
Read ahead sectors     auto
- currently set to     256
Block device           253:0
  2.减少/home分区空间
  # 释放 /dev/centos/home 分区 300G 的空间
  # 命令设置 /dev/centos/home 分区 200G空间
  $ lvreduce -L 200G /dev/centos/home
  WARNING: Reducing active logical volume to 200.00 GiB.
  THIS MAY DESTROY YOUR DATA (filesystem etc.)
  Do you really want to reduce centos/home? [y/n]: y
  Size of logical volume centos/home changed from 475.70 GiB (121778 extents) to 200.00 GiB (51200 extents).
  Logical volume centos/home successfully resized.
  3.增加/root分区空间
  $ lvextend -l +FREE /dev/centos/root
  Size of logical volume centos/root changed from 50.06 GiB (12816 extents) to 325.76 GiB (83394 extents).
  Logical volume centos/root successfully resized.
  4.扩展XFS文件空间大小
$ xfs_growfs /dev/mapper/centos-root
meta-data=/dev/mapper/centos-root isize=256    agcount=4, agsize=3276800 blks
=                       sectsz=512   attr=2, projid32bit=1
=                       crc=0        finobt=0 spinodes=0
data     =                       bsize=4096   blocks=13107200, imaxpct=25
=                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=0
log      =internal               bsize=4096   blocks=6400, version=2
=                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
data blocks changed from 13107200 to 85395456
  完成