How to Extend a Disk on Windows Server (Disk Management & DiskPart)

You upgraded the disk on your Windows Server VDS in the KavesNET panel, but C: still shows the old size? The new space is sitting unallocated — a few clicks away. This guide shows both GUI (Disk Management) and PowerShell (DiskPart) methods.

First: backup

Always take a backup/snapshot before disk operations. The KavesNET panel offers snapshots.

Method 1: Disk Management (GUI) — easy way

1. Rescan disks

Win + R → diskmgmt.msc → Enter

From the top menu: Action → Rescan Disks

2. Find the unallocated space

To the right of C: you’ll see new space marked “Unallocated”. If not, rescan again.

3. Extend the C: drive

Right-click C: → Extend Volume…

Wizard:

• Next → select all unallocated → Next → Finish

C: grows to its new size in seconds. No reboot needed, no downtime.

Method 2: DiskPart (CLI) — if no RDP

1. Open PowerShell as administrator

diskpart

2. List and select disk

list disk
select disk 0
list partition

3. Select partition and extend

select partition 2     # C: partition (usually 2 or 3)
extend
exit

extend uses all free space. For a specific size: extend size=10240 (10 GB in MB).

Modern PowerShell (cleaner)

Instead of DiskPart:

# Add unallocated to C:
$MaxSize = (Get-PartitionSupportedSize -DriveLetter C).SizeMax
Resize-Partition -DriveLetter C -Size $MaxSize

One line. Scriptable and safer.

Adding a new disk (alternative)

To add a new disk as D: instead of growing C::

1. Open Disk Management
2. New disk shows as Offline → right-click → Online
3. Right-click → Initialize Disk → choose GPT
4. Right-click unallocated → New Simple Volume → wizard:
   • Drive letter: D:
   • Filesystem: NTFS
   • Allocation unit: Default
   • Quick format

Common errors

• “Extend Volume” greyed out:
  • Unallocated space isn’t immediately to the right of C: (another partition is in between — must delete it first)
  • Disk is MBR and C: is already 2 TB — needs to be converted to GPT
• “Cannot extend a non-NTFS partition”: For ReFS/FAT32, use 3rd-party tools (AOMEI, EaseUS)
• New space doesn’t appear at all: Disk wasn’t actually grown on hypervisor side — open a KavesNET ticket
• Server’s recovery partition behind C:: Delete that partition first (after backup)

Doing it remotely (no RDP)

If you can’t RDP, open a VNC console from the KavesNET panel and run PowerShell there.

Performance tip

When C: fills, Windows slows down — keep 20 GB+ free especially for Windows Update. A Task Scheduler rule for disk alerts:

# Email if C: > 85%
$threshold = 85
$disk = Get-PSDrive C
$used = [math]::Round((($disk.Used / ($disk.Used + $disk.Free)) * 100), 1)
if ($used -gt $threshold) {
    Send-MailMessage -To "[email protected]" -From "[email protected]" `
        -Subject "Disk full alert: $used%" -SmtpServer "smtp.example.com"
}

For scheduling: see our Cron / Scheduled Task post.

Conclusion

Windows disk extension is a 2-minute job — Disk Management or one PowerShell line. After a KavesNET disk upgrade, you can do it immediately.

Related: Linux Disk Extension · Server Backups