[Linux Fundamentals #7] Expanding LVM: Resizing Storage Without the Drama

(For the Korean version, click here)

In our last post, we covered the basics of LVM. Today, we’re diving into the “killer feature” of LVM: Online Expansion.

If you’re a sysadmin, you’ve probably heard this before: “The /data partition is at 90%! We need more space ASAP!” In the old days, this was a total nightmare—backing up data, swapping drives, and downtime. With LVM, it’s a different story. You just plug in a new drive and “merge” it into your existing partition while the server is live. No downtime, no data loss.

Today, we’ll expand our existing /data area by adding a new 5GB hard drive.

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1. Prep the New Disk (fdisk)

Once your new disk (let’s say /dev/sdc) is detected by the system, we need to set the partition type to LVM, just like we did before.

# Check if sdc is detected
lsblk

# Start partitioning
fdisk /dev/sdc

The “Magic” Key Sequence:

1. n : Create a new partition.
2. p : Primary partition.
3. 1 : Partition number 1.
4. Enter twice : Use the full capacity.
5. t : Change the type (Don’t skip this!).
6. 8e : The hex code for Linux LVM.
7. w : Save and exit.

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2. Grow the Pool (vgextend)

Now, we take that new physical resource and add it to our existing virtual pool, datavg. Think of it as adding more water to a tank.

# 1. Initialize the new partition as a PV
pvcreate /dev/sdc1

# 2. Add the new PV to the existing VG (datavg)
vgextend datavg /dev/sdc1

# 3. Check if the VG capacity actually increased (Look at 'Free PE')
vgs

The pool (VG) is now larger, but the actual volume (datalv) you’re using hasn’t changed yet.

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3. Grow the Volume (lvextend)

The tank is bigger, so let’s actually expand the “pipe” or the volume we’re using. We’ll pour all that new space into datalv.

Bash

# Pour all the remaining free space in datavg into datalv
lvextend -l +100%FREE /dev/datavg/datalv

# Verify the new size
lvs

LVM-wise, you’re done. But if you run df -h, you’ll notice the size still looks the same. There’s one more step.

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4. Tell the File System (xfs_growfs)

The disk structure is now larger, but the file system (XFS) is still “living in the past.” We need to tell the file system to “grow” into the new space.

# Grow the XFS file system (This works while it's still mounted!)
xfs_growfs /data

# Final verification
df -h

Note: If you are using EXT4 instead of XFS, use resize2fs /dev/datavg/datalv.

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💡 An Engineer’s Take

“The best part about this is that it’s all done ‘online.’ No reboots, no maintenance windows. In cloud environments, you simply attach a volume in the console and run these few commands in the OS. It’s one of the most powerful tools in an engineer’s kit.”

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🚀 What’s Next?

Now you can build and expand LVM like a pro. But to complete the cycle, you have to know how to tear it down safely. In [Linux Basics #8], we’ll wrap up the series by learning how to properly delete LVM volumes without trashing the system. Stay tuned!