Logical volume management which named lvm allows you to decrease or increase the size of the logical volume and also filesystem. I 'll try to explain how to decrease logical volume size and also Filesystem size on this KB.
Which command we will use;
Step 1: First take a full backup of your filesystem
As is always the firsts case before start operation take a full backup of your filesystem whenever you perform a shrink or extend on filesystem logical volume etc.If you will perform this operation on a mounted filesystem like "/app" which is separated from root vg or another mount point you should just umount filesystem and continue operation.
On the other hand, if you will shrink root filesystem you should open your system on Boot CD. Almost all versions of the Linux bring-up volume group on boot automatically but if not you should use "vgchange" command.
#vgchange -a y vgname
This command set will activate the volume group.
Step 2:Start and force a filesystem check
This option is recommended. You should check if your filesystem is clear.
#e2fsck -f /dev/vgroot/lvroot
Step 3:Resize your filesystem before resize your Logical Volume
*This step is too critical. You should resize your filesystem then shrink the logical volume.
Set the new size of the filesystem. But be careful when you set new filesystem size. You should give new size bigger than file system usage. For example, if your filesystem size is 250 GB and usage is 170GB. So you should shrink new volume 180Gb. This value musn't be less than usage! And also if your logical volume will be set 200GB it's recommended to set filesystem size 180GB.
#resize2fs /dev/vgroot/lvroot 180G
Step 4: Reduce LVM size
After resizing filesystem now start the same operation for LVM. But set LVM size bigger than Filesystem size. In my case it'll be 200GB.
#lvreduce -L 200G /dev/vgroot/lvroot
Step 5: Re-run resize2fs