How to Fix an Azure VM Data Disk Missing After Resize

You resized your Azure VM data disk. The Azure portal shows the new size. But inside the VM, the drive still shows the old capacity, appears as unallocated space, or disappears from File Explorer altogether.

This issue usually looks worse than it is. In most cases, Azure has already expanded the managed disk, but the guest OS has not fully picked up the change yet. You need to confirm the resize, rescan the disk, and then extend the partition so Windows or Linux can use the extra space.

Microsoft’s current guidance also notes that some data-disk expansions can be done without downtime, while others still require the VM to be deallocated first.

In this guide, I’ll show you exactly how to fix an Azure VM data disk that looks missing or stuck after resize, with working steps for both Windows and Linux.

Why an Azure VM Disk Looks Missing After Resize

When you increase a managed disk in Azure, the change happens at the Azure storage layer first. The operating system inside the VM still needs to detect the new disk size. After that, the existing partition must be extended into the newly available space. Microsoft documents this as a separate OS-side step after the Azure resize is complete.

That means the problem usually happens at one of these stages:

1. The Azure disk resize did not fully apply.
2. The VM has not rescanned the disk yet.
3. The disk came back offline in Windows.
4. The partition was never extended.
5. The disk uses MBR, which cannot use space beyond 2 TB.

So the disk is often not lost. The OS just is not using the extra space yet.

Before You Fix Anything, Confirm the Azure Resize Completed

Start in the Azure portal before making OS-level changes.

1. Open Azure Portal.
2. Go to Virtual Machines.
3. Select the affected VM.
4. Open Disks.
5. Click the data disk you resized.
6. Open Size + performance.
7. Confirm the new disk size is shown there.

If the portal still shows the old size, do not waste time inside the VM yet. The Azure-side resize is the real problem.

Tip: Some Azure data disks support resizing without downtime, but this depends on the disk type—otherwise, you must stop and deallocate the VM before resizing. The updated size can take up to 10 minutes to appear inside the OS.

So if the resize was recent, wait a few minutes and rescan again before assuming something is broken.

How to Fix the Disk in Windows

If your Azure VM runs Windows Server or Windows client, work through these fixes in order.

Fix 1: Rescan Disks in Disk Management

This is the most common fix.

1. Connect to the VM with RDP.
2. Press Windows + R.
3. Type diskmgmt.msc and press Enter.
4. In Disk Management, click Action.
5. Select Rescan Disks.
6. Wait a few seconds and check the disk again.

If the resize has reached the VM, the disk should now show the larger capacity, usually with unallocated space at the end. Microsoft specifically notes that Windows VMs may need a rescan after disk expansion.

Fix 2: Bring the Disk Online if It Shows Offline

Sometimes the disk is present but offline, so it never appears in File Explorer.

In Disk Management:

1. Find the affected disk.
2. Look for a status like Offline.
3. Right-click the disk.
4. Click Online.

If the disk keeps going offline after reboot, check SAN policy with diskpart:

diskpart
san
san policy=OnlineAll
exit

This is more common on older Windows Server builds or templates.

Fix 3: Extend the Partition Into the New Space

If the disk shows the new size but part of it is unallocated, the resize succeeded. You now just need to extend the volume.

Using Disk Management

1. Open Disk Management.
2. Right-click the existing data volume.
3. Click Extend Volume.
4. Follow the wizard and use the available unallocated space.
5. Finish the wizard.

Using DiskPart

If Extend Volume is greyed out, use DiskPart instead:

diskpart
list volume
select volume <your-volume-number>
extend
exit

Microsoft states that the extend command preserves data, but for basic volumes the free space must be contiguous and on the same disk. It also requires NTFS for this workflow.

Fix 4: Check if the Disk Is MBR and Stuck at 2 TB

If you resized the disk beyond 2 TB and Windows still cannot use the full capacity, check the partition style.

MBR disks are limited to 2 TB or smaller. GPT supports larger disks and is the recommended partition style for larger drives.

To check:

1. Open Disk Management.
2. Right-click the disk label on the left.
3. Click Properties.
4. Open the Volumes tab.
5. Look at Partition style.

If it says MBR, that is likely the reason the extra space is unavailable.

Note: Do not use MBR2GPT for a normal data disk, as it only supports system disks; instead, back up your data, delete the volume, convert the disk to GPT, and recreate the partition before restoring data.

So, if your Azure data disk is MBR and you need more than 2 TB, the safe path is:

1. Back up the disk data.
2. Delete the volume or move the data off the disk.
3. Convert the disk to GPT.
4. Recreate the partition.
5. Restore the data.

That is the correct approach for a data disk.

Fix 5: Deallocate the VM and Resize Again

If the Azure portal still acts inconsistent, or the VM never detects the new size, repeat the resize the right way.

1. In Azure Portal, open the VM.
2. Click Stop.
3. Wait until the status shows Stopped (deallocated).
4. Go back to Disks.
5. Open the data disk.
6. Open Size + performance.
7. Apply the new size again.
8. Start the VM.
9. Rescan disks inside Windows.

Microsoft explicitly distinguishes a real Azure deallocation from a normal OS restart. A guest restart is not the same thing.

How to Fix the Disk in Linux

If your Azure VM runs Linux, the process is similar, but the commands are different.

Microsoft’s Linux guidance covers expanding both OS disks and data disks, and notes that Linux VMs may need a rescan after the managed disk is expanded.

Step 1: Confirm the Disk Size in the OS

SSH into the VM and run:

lsblk

This shows the current disk and partition layout.

You can also use:

sudo fdisk -l

Use these commands carefully and verify the correct disk name before changing anything.

Step 2: Rescan the Disk

Replace sdc with your actual disk name:

echo 1 | sudo tee /sys/class/block/sdc/device/rescan

After that, run lsblk again and check whether the raw disk size has increased.

Step 3: Expand the Partition

If the disk is larger but the partition is still the old size, grow the partition.

Example:

sudo growpart /dev/sdc 1

This example expands partition 1 on /dev/sdc.

Step 4: Resize the Filesystem

Now resize the filesystem so Linux can use the new space.

For ext4:

sudo resize2fs /dev/sdc1

For XFS, grow the mounted filesystem instead:

sudo xfs_growfs /mountpoint

Microsoft’s Linux documentation supports this general flow: expand the managed disk, rescan, extend the partition, then resize the filesystem.

Important Linux Tip

Double-check all three of these before running commands:

• the correct disk name, such as /dev/sdc
• the correct partition number, such as 1
• the correct filesystem type, such as ext4 or xfs

Running the wrong command on the wrong disk can damage the wrong volume.

Azure Disk Issues and Quick Fix Solutions

FAQs: Common Mistakes During Azure Disk Resize

Does Azure automatically extend the partition after resizing?

No, Azure only expands the managed disk. You still need to manually extend the partition or filesystem inside the VM.

Is restarting the VM enough after resizing a disk?

No, a normal restart is not the same as deallocating the VM. Some resize operations require a full stop and deallocation in Azure.

Can I use MBR2GPT to convert a data disk?

No, MBR2GPT only works for system disks. For data disks, you must back up data, convert to GPT properly, and then restore.

Why does my Linux disk show the same size after resize?

Because only the disk size changed. You still need to expand the partition and resize the filesystem to use the new space.

Why is my Azure disk showing as unallocated space after resize?

This means the resize worked, but the partition was not extended. You need to extend the volume to use the unallocated space.

Why is my Azure disk not showing in File Explorer after resize?

The disk may be offline in Disk Management. Bring it online, and it should appear normally in File Explorer.

When to Contact Azure Support

You should escalate the issue if:

• the Azure portal never updates the disk size
• the disk shows corruption or filesystem errors
• the VM has a specialized disk setup
• the disk disappears entirely after correct rescan and partition checks
• the VM becomes unstable after the resize

At that point, collect the VM name, disk name, subscription details, and screenshots of the Azure disk size versus the guest OS view.