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Athreya aka Maneshwar
Athreya aka Maneshwar

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Expanding Disk Size in Google Cloud

#webdev #programming #googlecloud #devops

Hi there! I'm Maneshwar. Right now, I’m building LiveAPI, a first-of-its-kind tool that helps you automatically index API endpoints across all your repositories. LiveAPI makes it easier to discover, understand, and interact with APIs in large infrastructures.

When your VM’s root disk is running out of space — say you're on 20GB and need to go to 40GB — here’s the exact procedure to scale the disk without breaking anything. This example uses an Ubuntu VM named phpbb-new.

Step 1: Resize the Disk from Google Cloud Console

  1. Go to Google Cloud Console.
  2. Navigate to Compute Engine → VM instances.
  3. Click your instance (e.g. phpbb-new).
  4. Scroll to the "Boot disk and local disks" section.
  5. Click the boot disk name.
  6. Click EDIT at the top.
  7. Change Size (GB) → from 20 → to 40.
  8. Hit SAVE.

Note: Disk size updates immediately in GCP, but the OS inside the VM still sees the old size. You’ll need to fix that next.

Step 2: SSH into the VM

From the instance details page, hit SSH.

Confirm you’re in with:

root@phpbb-new:~#
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Step 3: Check the Current Disk Usage

Run:

df -h
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You’ll likely see:

Filesystem      Size  Used Avail Use% Mounted on
/dev/root        19G   16G  3.1G  84% /
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Then run:

sudo fdisk -l
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Check that it detects the new disk size:

Disk /dev/sda: 40 GiB
...
GPT PMBR size mismatch (old size vs new size)
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Step 4: Fix the GPT Partition Table

Let’s correct the partition table to reflect the new size.

sudo fdisk /dev/sda
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At the Command (m for help): prompt, just type:

w
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This writes the updated partition layout and exits. Ignore any "device busy" warnings — it's fine in GCP.

Step 5: Expand the Partition

Run:

sudo growpart /dev/sda 1
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This resizes partition 1 (/dev/sda1), which maps to /.

Expected output:

CHANGED: partition=1 ... new: size=83883903
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Step 6: Resize the Filesystem

Tell ext4 to use the new space:

sudo resize2fs /dev/sda1
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This might take a few seconds. When it’s done, your root filesystem now uses the full disk.

Step 7: Verify It Worked

Final check:

df -h
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You should now see:

Filesystem      Size  Used Avail Use% Mounted on
/dev/root        39G   16G   22G  43% /
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Mission accomplished.

Recap: Quick Command List 

# SSH into VM
df -h
sudo fdisk -l

# Fix GPT table
sudo fdisk /dev/sda
# then just type: w

# Resize partition
sudo growpart /dev/sda 1

# Resize filesystem
sudo resize2fs /dev/sda1

# Verify
df -h
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Pro Tips

  • Works only for disks using GPT (which is default in GCP).
  • If your root disk is XFS instead of ext4, use xfs_growfs / instead of resize2fs.
  • For automated workflows, you can script this and run via cloud-init or startup scripts.

Done. Disk doubled. No reboot. No downtime.

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Top comments (1)

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shiva_shanker_k profile image
shiva shanker • • Edited

Honestly, there's gotta be a simpler way than all these manual steps! What about just using Google Cloud's auto-resize feature or setting up disk monitoring with alerts?
Sometimes the "simple" solution is just avoiding the problem entirely.what's your opinion in this!!