How does linux resize partitions without loss

Situation:

home: 500 G root: 50 G The root partition is insufficient

Idea: Divide the space of home into root

#  Set up the home Partition size is 200G Release, 300G space 
$ lvreduce -L 200G /dev/centos/home

#  Expand the free space to root partition 
$ lvextend -l +100%FREE /dev/centos/root

#  use XFS The file system comes with a command set that increases partition space 
$ xfs_growfs /dev/mapper/centos-root

The instance

situation

The partition /dev/mapper/ centos-ES22en mounted in the root directory is full, occupying 100%

$ df -h
Filesystem        Size Used Avail Use% Mounted on
/dev/mapper/centos-root  50G  50G  19M 100% /
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

The partition space mounted in the root directory is too small, only 50G, while the server home directory is a very useful directory, hanging in nearly 500G space.

Idea: Partition from ES34en-ES35en 300G to ES37en-ES38en.

operation

1. View the partition information

$ 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. Reduction of /home partition space

#  The release of  /dev/centos/home  partition  300G  The space of 
#  Command to set  /dev/centos/home  partition  200G space 
$ 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. Increase of /root partition space

$ lvextend -l +100%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. Expand the XFS file space size

$ 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

complete