OS Disk Partition Expansion Failure in Azure VM

The screenshots show the exact blocking condition: a Recovery partition sits between C: and the new unallocated space. Windows can extend an NTFS volume only into adjacent unallocated space, so Extend Volume is unavailable until that Recovery partition is removed.

Recommended approach:

1. Take a snapshot of the OS disk first
   • In the Azure portal, open the OS disk resource.
   • Select Snapshots > Create snapshot.
   • This is important because deleting partitions is a destructive operation.
2. Connect to the VM
   • Use RDP or, if needed, Azure Serial Console.
3. Open Command Prompt as Administrator
4. Use DiskPart to confirm the partition layout

      diskpart
      list disk
      select disk 0
      list partition
   

   Expected result: the OS partition is followed by a small Recovery partition, and then the unallocated space.
5. Delete the Recovery partition Select the recovery partition number shown in list partition, then run:

      select partition 2
      delete partition override
   

   If your Recovery partition is a different number, use that number instead. The override option is required because Recovery partitions are protected.
6. Exit DiskPart

      exit
   

7. Extend C: in Disk Management
   • Press Windows+R
   • Run diskmgmt.msc
   • Right-click C:
   • Select Extend Volume
   • Complete the wizard to use the unallocated space
8. Verify the result
   • In Disk Management, confirm that C: now reflects the expanded size.
   • In File Explorer, confirm the free space increased.
   • Optional admin command:

      wmic logicaldisk get size,freespace,caption
   

If RDP access is unavailable, the documented fallback is to attach the OS disk to a repair VM and perform the same DiskPart steps there, then restore it back.

Additional checks if extension still fails:

• If the disk uses MBR, the maximum partition size is 2 TB.
• If Azure Disk Encryption (ADE) changed the partition layout, the resolution is different because a System Reserved partition can block the extension instead of a Recovery partition.

References:

• Can't extend an OS volume because a recovery partition blocks the extension
• Expand virtual hard disks attached to a Windows virtual machine
• Can't extend a volume on an Azure Windows VM
• Cannot extend an encrypted OS volume in Windows