Extend LVM Partition Without Downtime by Adding a New Disk (PV)

Problem Overview

In production systems, disk space can run out unexpectedly. Restarting servers to increase disk space is often not an option, especially for critical applications.
Linux LVM (Logical Volume Manager) allows you to extend storage online, without stopping services or rebooting the server.
In this guide, you’ll learn how to safely extend an LVM partition step by step while the system remains up and running.
This approach is widely used in enterprise environments and is a must-know skill for Linux administrators and DevOps engineers.

⚠️ Important Note: Do Not Shrink the Root Filesystem

Shrinking the root (/) filesystem is not recommended and is unsafe in real-world environments. The root volume is designed to be extended, not reduced. Once you increase the root filesystem, do not attempt to shrink it.
Attempting to shrink / can lead to filesystem corruption, and in many cases the system may fail to boot after a restart. Recovering such a system is extremely difficult and may even be impossible without a full rebuild.

Prerequisites

Before starting, make sure the following conditions are met:

The system is using LVM
A new disk has been attached to the server
You have root or sudo access
Filesystem is ext4 or xfs
You have verified current disk usage using the command df -h and lsblk

Solution

Confirm that the OS detects the newly added disk. You should see the new disk (for example /dev/sdb) without any partitions.

[root@pythonlinuxhub ~]# lsblk
NAME             MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
sda                8:0    0   20G  0 disk
├─sda1             8:1    0    1G  0 part /boot
└─sda2             8:2    0   19G  0 part
  ├─rhel_10-root 253:0    0   17G  0 lvm  /
  └─rhel_10-swap 253:1    0    2G  0 lvm  [SWAP]
sdb                8:16   0    4G  0 disk
sr0               11:0    1 1024M  0 rom

Initialize the new disk as an LVM physical volume.

root@pythonlinuxhub ~]# pvcreate /dev/sdb
  Physical volume "/dev/sdb" successfully created.
[root@pythonlinuxhub ~]# pvs
  PV         VG      Fmt  Attr PSize   PFree
  /dev/sda2  rhel_10 lvm2 a--  <19.00g    0
  /dev/sdb           lvm2 ---    4.00g 4.00g

Add the new physical volume to the existing volume group.

[root@pythonlinuxhub ~]# vgextend rhel_10 /dev/sdb
  Volume group "rhel_10" successfully extended
[root@pythonlinuxhub ~]# vgs
  VG      #PV #LV #SN Attr   VSize  VFree
  rhel_10   2   2   0 wz--n- 22.99g <4.00g
[root@pythonlinuxhub ~]#

You should now see additional free space available in the volume group.

Extend the logical volume using all available free space.

[root@pythonlinuxhub ~]# lvs
  LV   VG      Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  root rhel_10 -wi-ao---- <17.00g
  swap rhel_10 -wi-ao----   2.00g
[root@pythonlinuxhub ~]# lvextend -l +100%FREE /dev/rhel_10/root
  Size of logical volume rhel_10/root changed from <17.00 GiB (4351 extents) to 20.99 GiB (5374 extents).
  Logical volume rhel_10/root successfully resized.
[root@pythonlinuxhub ~]# lvs
  LV   VG      Attr       LSize  Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  root rhel_10 -wi-ao---- 20.99g
  swap rhel_10 -wi-ao----  2.00g

At this stage, the logical volume is extended, but the filesystem is not yet resized.
Resize the filesystem
- For ext4 Filesystem
  - ```
  [root@pythonlinuxhub ~]# resize2fs /dev/rhel_10/root
```
- For xfs Filesystem
  - ```
  [root@pythonlinuxhub ~]# xfs_growfs /
```
- XFS requires the mount point, not the device path.

Verify the updated disk space. You should now see the increased space reflected on the mounted filesystem.

[root@pythonlinuxhub ~]# df -h
Filesystem                Size  Used Avail Use% Mounted on
devtmpfs                  4.0M     0  4.0M   0% /dev
tmpfs                     1.8G     0  1.8G   0% /dev/shm
tmpfs                     732M  9.3M  722M   2% /run
/dev/mapper/rhel_10-root   21G  8.2G   13G  39% /
/dev/sda1                 960M  372M  589M  39% /boot
tmpfs                     366M   96K  366M   1% /run/user/1000

[root@pythonlinuxhub ~]# lsblk
NAME             MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
sda                8:0    0   20G  0 disk
├─sda1             8:1    0    1G  0 part /boot
└─sda2             8:2    0   19G  0 part
  ├─rhel_10-root 253:0    0   21G  0 lvm  /
  └─rhel_10-swap 253:1    0    2G  0 lvm  [SWAP]
sdb                8:16   0    4G  0 disk
└─rhel_10-root   253:0    0   21G  0 lvm  /
sr0               11:0    1 1024M  0 rom