Resizing an LVM Disk for the Root Mountpoint

Introduction

Logical Volume Manager (LVM) provides flexible disk management, allowing you to resize storage without downtime. This guide explains how to resize the LVM disk for the root (/) mountpoint on a Linux system, typically used with KVM virtual machines. We’ll add a new disk, extend the volume group, and resize the logical volume to increase the root filesystem’s capacity.

Environment

• Operating System: Linux (e.g., CentOS, Rocky Linux, Ubuntu).
• Virtualization: KVM (optional, for adding disks to VMs).
• Disk Type: LVM (Logical Volume Manager).
• Mountpoint: Root (/).

Prerequisites

Before resizing, verify the current disk configuration, mountpoints, and LVM details using:

lsblk -p

Example output:

NAME                        MAJ:MIN RM    SIZE RO TYPE MOUNTPOINT
/dev/sr0                     11:0    1   1024M  0 rom
/dev/vda                    252:0    0    200G  0 disk
├─/dev/vda1                 252:1    0    200M  0 part /boot/efi
├─/dev/vda2                 252:2    0      1G  0 part /boot
└─/dev/vda3                 252:3    0  198.8G  0 part
  ├─/dev/mapper/centos-root 253:0    0   88.8G  0 lvm  /
  └─/dev/mapper/centos-swap 253:1    0     10G  0 lvm  [SWAP]
/dev/vdb                    252:16   0  500.1G  0 disk
├─/dev/vdb1                 252:17   0  186.3G  0 part /home
└─/dev/vdb2                 252:18   0  313.8G  0 part /log
/dev/vdc                    252:32   0 1000.2G  0 disk
└─/dev/vdc1                 252:33   0 1000.2G  0 part /data

• Key Information:
  • Mountpoint: / (root).
  • LVM Path: /dev/mapper/centos-root.
  • Volume Group: Likely centos (to be confirmed).
  • Disk: New disk will be added (e.g., /dev/vdd).

Note: Always back up critical data before modifying disks to prevent data loss.

Steps

Step 1 - Add a New Disk

For LVM resizing, adding a new disk is recommended to provide additional space. If using KVM:

• Access the VM’s management interface (e.g., virt-manager or virsh).
• Add a new virtual disk with the desired size (e.g., 100 GB) to the VM.
• Ensure the VM recognizes the new disk after rebooting or hot-adding.

Note: Choose a disk size that meets your capacity needs.

Step 2 - Verify the New Disk

Check the new disk’s path using:

lsblk -p

• Example: If the new disk appears as /dev/vdd, note its path.
• If the disk isn’t visible, rescan the bus:

  echo "- - -" | sudo tee /sys/class/scsi_host/hostX/scan

  (Replace hostX with the appropriate SCSI host, e.g., host0.)

Step 3 - Create a Physical Volume

Initialize the new disk as a physical volume (PV) for LVM:

sudo pvcreate <new-disk-path>

• Example: sudo pvcreate /dev/vdd
• This prepares the disk for use in an LVM volume group.

Step 4 - Identify the Volume Group

List the existing volume groups to find the one associated with the root filesystem:

sudo vgs

Example output:

  VG     #PV #LV #SN Attr   VSize   VFree
  centos   1   2   0 wz--n- 198.80g 100.00g

• The volume group (VG) name is centos (from /dev/mapper/centos-root).

Step 5 - Extend the Volume Group

Add the new physical volume to the existing volume group:

sudo vgextend <volume-group-name> <new-disk-path>

• Example: sudo vgextend centos /dev/vdd
• This increases the VG’s capacity by incorporating the new disk.

Step 6 - Verify Volume Group Changes

Check the volume group to confirm the new physical volume was added:

sudo vgs

Or, for more details:

sudo vgdisplay

Example output:

  --- Volume group ---
  VG Name               centos
  ...
  VG Size               298.80 GiB
  PE Size               4.00 MiB
  Total PE              76544
  Free  PE              25600
  Alloc PE / Size       50944 / 198.80 GiB
  PV Count              2

• PV Count: 2 confirms the new disk was added.

Step 7 - Identify the Logical Volume

List logical volumes to find the one for the root mountpoint:

sudo lvs

Or, for details:

sudo lvdisplay

Example output:

  --- Logical volume ---
  LV Path                /dev/centos/root
  LV Name                root
  VG Name                centos
  LV Size                88.80 GiB

• The logical volume (LV) path is /dev/centos/root.

Step 8 - Extend the Logical Volume

Extend the logical volume to use all available space in the volume group:

sudo lvextend -l +100%FREE <logical-volume-path>

• Example: sudo lvextend -l +100%FREE /dev/centos/root
• -l +100%FREE: Allocates all free space in the VG to the LV.

Step 9 - Resize the Filesystem

Update the filesystem to recognize the new LV size. For XFS (common on CentOS/RHEL):

sudo xfs_growfs <mountpoint>

• Example: sudo xfs_growfs /
• If using ext4, use:

  sudo resize2fs <logical-volume-path>

  • Example: sudo resize2fs /dev/centos/root

This step adjusts the filesystem to use the expanded space.

Step 10 - Verify the New Size

Confirm the resized disk size:

df -kh

Example output:

Filesystem                 Size  Used Avail Use% Mounted on
/dev/mapper/centos-root    188G  5.0G  183G   3% /

Or:

lsblk -p

Example output:

NAME                        MAJ:MIN RM    SIZE RO TYPE MOUNTPOINT
/dev/vda                    252:0    0    200G  0 disk
├─/dev/vda1                 252:1    0    200M  0 part /boot/efi
├─/dev/vda2                 252:2    0      1G  0 part /boot
└─/dev/vda3                 252:3    0  198.8G  0 part
  ├─/dev/mapper/centos-root 253:0    0   188.8G  0 lvm  /
  └─/dev/mapper/centos-swap 253:1    0     10G  0 lvm  [SWAP]
/dev/vdd                    252:48   0    100G  0 disk

• The root filesystem (/dev/mapper/centos-root) now reflects the increased size.

Notes

• Backup First: Always back up data before resizing to avoid loss.
• Filesystem Type: Confirm the filesystem type (xfs or ext4) with df -T. Use the appropriate resize command.
• KVM Disk Addition: If not using KVM, add a physical disk to a bare-metal server and rescan as needed.
• Error Handling: If pvcreate fails, ensure the disk is not partitioned (fdisk to remove partitions if needed).

Related Scripts

• Content under construction