Extend existing logical volumes - Learn Tech From Zero

6. Create and Configure File Systems

📘Red Hat Certified System Administrator (RHCSA – EX200)

In Linux, Logical Volumes (LVs) are flexible storage units that sit on top of Volume Groups (VGs), which in turn sit on Physical Volumes (PVs). Sometimes, a logical volume may run out of space. Instead of creating a new disk or partition, Linux allows you to extend the size of an existing logical volume dynamically.

This is a common task in IT environments, for example:

Expanding storage for a database that is running out of space.
Increasing disk space for virtual machines in a virtualization environment.
Adding space to a home directory on a server.

1. Check Current Logical Volume Status

Before extending an LV, you need to know:

The name of the logical volume.
Its size.
The free space available in the Volume Group.

Commands to use:

# List all logical volumes
sudo lvdisplay# Check free space in the volume group
sudo vgdisplay

Key points to note:

LV Name → the name of the logical volume you want to extend.
VG Name → the volume group that contains the LV.
Free PE / Size → how much free space is available in the volume group. You cannot extend beyond this.

2. Extend the Logical Volume

You can extend an LV using either absolute size or by adding a certain amount of space.

Option A: Extend by Size

To add a specific size (for example, 10 GB):

sudo lvextend -L +10G /dev/<VG_Name>/<LV_Name>

-L +10G → adds 10 GB to the existing size.
/dev/<VG_Name>/<LV_Name> → the path to the logical volume.

Option B: Extend to Maximum Available Space

To use all free space in the volume group:

sudo lvextend -l +100%FREE /dev/<VG_Name>/<LV_Name>

-l +100%FREE → adds all remaining free extents in the volume group to the LV.

3. Resize the Filesystem

After extending the LV, the filesystem on it must also be resized so the OS can use the new space.

The command depends on the filesystem type:

A. Ext4 Filesystem

sudo resize2fs /dev/<VG_Name>/<LV_Name>

B. XFS Filesystem

sudo xfs_growfs /mount/point

For XFS, you specify the mount point, not the device path.
You can extend mounted filesystems online without unmounting, which is useful for servers.

4. Verify the Extension

After extending the LV and filesystem, confirm that the new size is reflected:

# Check LV size
sudo lvdisplay /dev/<VG_Name>/<LV_Name># Check filesystem size
df -h

Example Output:

Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg1-lv1    30G   15G   15G  50% /data

5. Important Exam Points

Command Options:
- lvextend -L +size → add specific size.
- lvextend -l +100%FREE → use all free space.
- resize2fs → for ext4.
- xfs_growfs → for XFS.
Order of Operations:
1. Check LV and VG sizes.
2. Extend the LV.
3. Resize the filesystem.
4. Verify changes.
You can extend mounted filesystems, especially XFS, which is common in modern Linux servers.
Cannot exceed the free space in the volume group.
Always check disk space and free extents before extending.

6. IT Environment Examples

Database Server: A MySQL database is filling up /var/lib/mysql. Admin extends the LV to prevent downtime.
VM Storage: A virtual machine’s logical disk grows in VMware or KVM. LV is extended so the VM can store more data.
Shared Network Storage: Fileserver /data LV extended when team project files grow.

7. Quick Summary Table

Step	Command Example	Notes
Check LV	`lvdisplay`	See LV size
Check VG free space	`vgdisplay`	See available space
Extend LV by 10GB	`lvextend -L +10G /dev/vg1/lv1`	Add specific size
Extend LV to all free space	`lvextend -l +100%FREE /dev/vg1/lv1`	Use max space
Resize ext4 FS	`resize2fs /dev/vg1/lv1`	Must do after LV extension
Resize XFS FS	`xfs_growfs /data`	Specify mount point
Verify	`df -h`	Confirm new space

✅ Exam Tip:
The exam may ask you to extend a logical volume and its filesystem. Remember, extending the LV alone does not automatically give you more usable space—you must also resize the filesystem.