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Resizing RHEL/AlmaLinux LVM Disk in Proxmox

Guide for expanding disk space on RHEL-based systems (RHEL, CentOS, AlmaLinux, Rocky Linux) running in Proxmox VMs after increasing the virtual disk size.

Overview​

After expanding a virtual disk in Proxmox, the guest operating system needs to be told to use the additional space. This guide covers the complete process for LVM-based systems.

Step 1: Verify New Disk Size​

After expanding the disk in Proxmox, check if the system recognizes the new size:

dmesg | grep sda

This shows kernel messages about the disk device and its detected size.

Step 2: Check Current Partition Layout​

View the current partition structure:

fdisk -l /dev/sda | grep ^/dev

This displays all partitions on the disk with their current sizes.

Step 3: Resize the LVM Partition​

Use parted to expand the partition (usually partition 2 on LVM systems):

parted /dev/sda

In the parted prompt:

print              # View current partition table
resizepart 2 100%  # Resize partition 2 to use 100% of disk
quit               # Exit parted
Partition Numbers

LVM typically uses partition 2 (/dev/sda2). Use print to confirm which partition number contains your LVM.

Step 4: Resize the Physical Volume​

Expand the LVM physical volume to use the newly resized partition:

pvresize /dev/sda2

This tells LVM that the physical volume now has more space available.

Step 5: Check Logical Volumes​

View all logical volumes and their current sizes:

lvdisplay

Take note of:

  • Volume group name (e.g., almalinux, rhel, cl)
  • Logical volume name (e.g., root, home)
  • Current size

Step 6: Resize Logical Volumes​

Option A: Add Specific Amount (GB)​

Add a fixed amount of space:

lvresize --size +20G --resizefs /dev/{volume_group_name}/root

Example:

lvresize --size +20G --resizefs /dev/almalinux/root

Option B: Use All Available Space​

Expand to use all free space in the volume group:

lvresize --extents +100%FREE --resizefs /dev/{volume_group_name}/home

Example:

lvresize --extents +100%FREE --resizefs /dev/almalinux/home
--resizefs Flag

The --resizefs flag automatically resizes the filesystem after expanding the logical volume. Without it, you'd need to run resize2fs (ext4) or xfs_growfs (xfs) manually.

Verification​

Check Disk Space​

Verify the new space is available:

df -h

Check LVM Status​

# Physical volumes
pvdisplay

# Volume groups
vgdisplay

# Logical volumes
lvdisplay

Complete Example Workflow​

Here's a complete example expanding a 50GB disk to 100GB:

# 1. Check new disk size
dmesg | grep sda

# 2. View current layout
fdisk -l /dev/sda | grep ^/dev

# 3. Resize partition
parted /dev/sda
print
resizepart 2 100%
quit

# 4. Resize physical volume
pvresize /dev/sda2

# 5. Check logical volumes
lvdisplay

# 6. Expand root to use all free space
lvresize --extents +100%FREE --resizefs /dev/almalinux/root

# 7. Verify
df -h

Troubleshooting​

Partition Not Resizing​

If resizepart fails:

# Try using fdisk instead
fdisk /dev/sda
# Delete and recreate the partition with same start sector but larger size
# WARNING: Note the exact start sector before deleting!

Filesystem Not Growing​

If --resizefs fails or you didn't use it:

For ext4:

resize2fs /dev/almalinux/root

For XFS:

xfs_growfs /dev/almalinux/root

No Free Space in Volume Group​

Check volume group:

vgdisplay

If "Free PE" shows 0, the physical volume wasn't resized properly. Rerun:

pvresize /dev/sda2

Disk Not Recognized​

If the VM doesn't see the new disk size:

  1. Rescan SCSI bus (without reboot):
echo 1 > /sys/class/scsi_device/0:0:0:0/device/rescan
  1. Or reboot the VM (safest option)

Multiple Logical Volumes​

If you have multiple LVs (e.g., /root and /home), decide which one gets the extra space:

# Give 30GB to root
lvresize --size +30G --resizefs /dev/almalinux/root

# Give remaining to home
lvresize --extents +100%FREE --resizefs /dev/almalinux/home

Best Practices​

  1. Backup First: Always backup important data before resizing
  2. Check Filesystem Type: Use appropriate resize command for your filesystem
  3. Plan Allocation: Decide which logical volume gets the extra space
  4. Test in Development: Practice on a test VM first
  5. Monitor Space: Use df -h regularly to monitor disk usage

Alternative: Extending in Proxmox GUI​

  1. Shutdown the VM (or use hot-plug if supported)
  2. Go to VM → Hardware → Hard Disk
  3. Click "Resize disk"
  4. Enter additional size
  5. Start VM and follow steps above

Common Volume Group Names​

  • RHEL: rhel or cl (CentOS Linux)
  • AlmaLinux: almalinux
  • Rocky Linux: rocky or rl
  • CentOS Stream: cs

Check with vgdisplay to confirm your exact name.

Removing Unnecessary Logical Volume​

Sometimes you may want to consolidate space by removing a separate logical volume (like /home) and merging it into root. This is useful when you don't need separate partitions.

Data Loss Warning

This process will DELETE ALL DATA on the logical volume being removed. Make sure you have backups or migrate data first!

Step-by-Step: Removing /home and Extending /root​

1. Backup Home Directory​

Create a temporary backup location and copy all home data:

sudo mkdir -p /media/home_backup
sudo cp -a /home/. /media/home_backup/

The -a flag preserves permissions, ownership, and timestamps.

2. Disable Home Volume in fstab​

Edit the filesystem table to prevent mounting the home volume:

sudo vi /etc/fstab

Find the line mounting /home and comment it out by adding # at the beginning:

# /dev/mapper/almalinux-home /home xfs defaults 0 0

3. Reboot the System​

Reboot to ensure the home volume is no longer mounted:

sudo reboot

4. Remove the Logical Volume​

After reboot, delete the home logical volume:

sudo lvremove /dev/mapper/almalinux-home

Type y to confirm deletion.

Volume Path

The exact path may vary. Use lvdisplay to find your volume group and logical volume names. Common formats:

  • /dev/mapper/almalinux-home
  • /dev/mapper/rhel-home
  • /dev/almalinux/home

5. Extend Root Volume​

Expand the root volume to use all freed space:

sudo lvextend -l +100%FREE -r /dev/mapper/almalinux-root

The -r flag automatically resizes the filesystem.

6. Restore Home Data​

Copy the backed-up home data back to /home:

sudo cp -a /media/home_backup/. /home/

7. Cleanup Backup​

Remove the temporary backup after verifying everything works:

sudo rm -rf /media/home_backup

Verification​

Check that the root partition now has more space:

df -h

Verify home data is accessible:

ls -la /home

Check user permissions:

ls -la /home/yourusername

When to Remove Separate Volumes​

Good reasons to consolidate:

  • Simple single-user systems
  • VMs with limited disk space
  • Easier management with one large partition
  • No need for separate quota management

Keep separate volumes when:

  • Multi-user environments
  • Need quota enforcement
  • Want to protect system from user data filling disk
  • Following corporate policies

Alternative: Just Shrink Home​

If you want to keep /home but give more space to root:

# Don't remove, just resize
sudo lvresize --size 10G --resizefs /dev/almalinux/home

# Give freed space to root
sudo lvextend -l +100%FREE -r /dev/almalinux/root

Additional Resources​