You can extend a volume size in linux by just following the commands below
If you want to extend a size of volume /dev/mapper/volume-var to 400GB you need enter the following command.
lvextend -L400GB /dev/mapper/volume-var
Extending logical volume var to 400.00 GiB Logical volume usr successfully resized
Then resize the volume
resize2fs 1.41.12 (17-May-2010) Filesystem at /dev/mapper/volume-var is mounted on /var; on-line resizing required old desc_blocks = 1, new_desc_blocks = 7 Performing an on-line resize of /dev/mapper/volume-var to 26214400 (4k) blocks. The filesystem on /dev/mapper/volume-var is now 26214400 blocks long.
You are done with lvm extending.
[Note: For /var and / partitions you will not be able to unmount them but you may resize the partition without unmounting and it is at your own risk of data loss].
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