How to Reduce a Logical Volume in GNU/Linux Using LVM

How to Reduce a Logical Volume in GNU/Linux Using LVM

Logical Volume Management is a vast improvement over standard partitioning schemes. Among many other things, it allows you to decrease the size of a volume without recreating it completely.

All of the required steps must be performed on an unmounted volume. If want to reduce the size of a non-root volume, simply unmount it. For a root volume, you’ll have to boot from a CD. Any modern live or rescue CD should work fine

In this article I will explain how to reduce the Logical Volume in Red Hat Linux system without loss of data.

STEPS:-

1.   Un mount the logical volume: 

umount /mnt/logical_volume1

Ex-

[root@server01 ~]# df -h

Filesystem            Size  Used Avail Use% Mounted on

/dev/mapper/VolGroup-lv_root     50G   26G   22G  55% /

tmpfs                                         7.8G     0  7.8G   0% /dev/shm

/dev/sda1                                            485M   32M  429M   7% /boot

/dev/mapper/VolGroup-lv_home  491G   55G  412G  12% /home

[root@server01 ~]# umount /home

If this file system is in use, Use the following commands to unmount partition forcefully.

[root@server01 ~]# fuser –km /home

[root@server01 ~]# umount  –f /home

2.   Make a backup of logical Volume.

Steps:

1. Check the size of the logical volume (LV Size): 

lvdisplay /dev/volume_group1/logical_volume1


Ex- 

--- Logical volume ---
LV Name /dev/mapper/VolGroup-lv_home
VG Name VolGroup
LV UUID AxihqP-Yt8l-5scY-bXNG-Bn5D-K3ms-X7v1Ys
LV Write Access read/write
LV Status available
# open 1
LV Size 200,00 GB
Current LE 6400
Segments 2
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 253:5

Usually, snapshots are smaller than the original logical volume, but I recommend to use at least the same space.

2. Create the snapshot: 

lvcreate -L200G -s -n backup_logical_volume1 /dev/volume_group1/logical_volume1

The -s param tells lvcreate to create a snapshot instead of a normal logical volume.

Ex-

lvcreate -L200G -s -n backup_logical_volume  /dev/mapper/VolGroup-lv_home

3.   Check the file system integrity: 

fsck -f -y -v /dev/volume_group1/logical_volume1

Ex-

[root@server01 ~]#   fsck -f -y -v /dev/mapper/VolGroup-lv_home

fsck from util-linux-ng 2.17.2

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

 2634206 inodes used (8.06%)

   62765 non-contiguous files (2.4%)

       7 non-contiguous directories (0.0%)

         # of inodes with ind/dind/tind blocks: 0/0/0

         Extent depth histogram: 2634192/4

16246730 blocks used (12.43%)

       0 bad blocks

       3 large files

 2589225 regular files

   44972 directories

       0 character device files

       0 block device files

       0 fifos

       0 links

       0 symbolic links (0 fast symbolic links)

       0 sockets

--------

 2634197 files

4.   Resize the file system to something smaller than the final size (around 190GB in this case): 

resize2fs /dev/volume_group1/logical_volume1 190G

This Step takes a long time to resize the volume.

Ex-

[root@server01 ~]# resize2fs /dev/mapper/VolGroup-lv_home 190G

resize2fs 1.41.12 (17-May-2010)

Resizing the filesystem on /dev/mapper/VolGroup-lv_home to 49807360 (4k) blocks.

The filesystem on /dev/mapper/VolGroup-lv_home is now 49807360 blocks long.

5.   Check the filesystem integrity again: 

fsck -f -y -v /dev/volume_group1/logical_volume1

Ex-

fsck -f -y –v /dev/mapper/VolGroup-lv_home

6.   Reduce the logical volume: 

lvreduce -L 85G /dev/volume_group1/logical_volume1

Ex-

[root@server01 ~]# lvreduce -L 195G /dev/mapper/VolGroup-lv_home

  WARNING: Reducing active logical volume to 195.00 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 195.00 GiB

  Logical volume lv_home successfully resized

7.   Resize the filesystem to fit the logical volume: 

resize2fs /dev/volume_group1/logical_volume1

Ex-

[root@server01 ~]# resize2fs /dev/mapper/VolGroup-lv_home

resize2fs 1.41.12 (17-May-2010)

Resizing the filesystem on /dev/mapper/VolGroup-lv_home to 51118080 (4k) blocks.

The filesystem on /dev/mapper/VolGroup-lv_home is now 51118080 blocks long.

8.   Check the filesystem to know whether the reduction went fine:

 fsck -f -y -v /dev/volume_group1/logical_volume1

Ex-

fsck -f -y –v /dev/mapper/VolGroup-lv_home

9.   Check the size of Logical Volume.

[root@server01 ~]# lvs

  LV      VG       Attr     LSize   Pool Origin Data%  Move Log Copy%  Convert

  lv_home VolGroup -wi-a--- 195.00g

  lv_root VolGroup -wi-ao--  50.00g

  lv_swap VolGroup -wi-ao--   7.84g

10.                Mount the logical volume: 

mount /mnt/logical_volume1

Ex-

mount  /dev/mapper/VolGroup-lv_home  /home

NOTE: if you aren’t careful with the disk space you are using and the final disk space you are going to be using, this operation can cause data loss. I recommend to backup the logical volume before the reduction and to use around 5GB of “safe space” while reducing the filesystem in order to avoid data loss.