Migrating an IBM Windows Server 2003 Physical Machine to Proxmox and Reducing Disk Size

This post documents the complete process of converting an old IBM physical server running Windows Server 2003 into a virtual machine on Proxmox VE, and then shrinking its 2 TB system disk down to a much smaller, space-efficient image.

1. P2V with VMware vCenter Converter (XP-Compatible Version)

Because the original system still ran within the Windows XP–era software environment, I used an older release of VMware vCenter Converter (P2V Virtual Machine Converter) — one of the few versions that still runs correctly on XP / Server 2003.

Steps

Install VMware vCenter Converter on the IBM host.
Choose Convert Local Machine.
Set the destination format to VMware Workstation / Other VMware Virtual Machine.
Export the resulting .vmdk files to an external drive or shared folder.

When finished, the converter produces a set of Windows2003.vmdk and .vmx files ready for further conversion.

2. Converting VMDK to Proxmox QCOW2

Copy the exported .vmdk file to the Proxmox storage path, for example:

/mnt/pve/nas2-in/images/602/

Then convert it to the QCOW2 format:

qemu-img convert -O qcow2 Windows2003.vmdk vm-602-disk-0.qcow2

Proxmox can now attach this QCOW2 disk directly.

3. First Boot Test

Create a new virtual machine (SeaBIOS, VGA display).
Attach vm-602-disk-0.qcow2 as the primary disk.
Boot and verify that Windows Server 2003 starts properly.
Check that IIS and custom applications still function.

If boot errors such as “NTLDR is missing” appear, boot from the Windows Server 2003 installation CD and run:

fixboot
fixmbr
bootcfg /rebuild

4. Preparing the System for Shrinking

The original disk size was 2 TB, but only around 50 GB was actually used.
Before reducing the virtual disk, the file system must be cleaned and unused blocks released.

4.1 Defragment the Disk

Run the built-in Disk Defragmenter inside Windows 2003 to move all data toward the beginning of the disk.

4.2 Zero Free Space with SDelete

Download Microsoft Sysinternals sdelete.exe and execute:

sdelete -z C:

This fills all free blocks with zeros so that later compression and trimming are effective.

Because the virtual disk was configured with an IDE interface, disk I/O was extremely slow.
In my case, SDelete took nearly two weeks to complete.
CPU and I/O utilization stayed at 100% throughout.
If you use VirtIO or SCSI storage instead, this step would finish in a few hours.

5. Shrinking the Partition in Windows 7

Windows Server 2003 cannot shrink a system partition natively.
Initially, I attempted to use Clonezilla and GParted Live, but both reported disk corruption or “invalid file system” errors and refused to resize the partition.
Even after running chkdsk /f back in Windows 2003, both tools continued to mis-detect the NTFS structure as damaged.
The issue appears to come from incompatibility between older NTFS metadata and the NTFS drivers shipped with those utilities.

The reliable workaround was to mount the QCOW2 disk inside a Windows 7 VM and use the native Disk Management utility:

Power off the Windows 2003 VM.
Attach its QCOW2 as a secondary disk to a Windows 7 VM.
Open Disk Management (diskmgmt.msc).
Right-click C: → Shrink Volume, and reduce it to about 49 GB.
The remaining space becomes Unallocated.

This approach worked perfectly and safely adjusted the NTFS partition size.

6. Trimming the QCOW2 Image in Proxmox

Attach the QCOW2 via NBD and verify the partition table:
```
qemu-nbd -r -c /dev/nbd0 vm-602-disk-0.qcow2
fdisk -l /dev/nbd0
```
/dev/nbd0p1 should report roughly 49 GB.
Disconnect the mapping:
```
qemu-nbd -d /dev/nbd0
```
Safely shrink the virtual disk (leave a small buffer):
```
qemu-img resize --shrink vm-602-disk-0.qcow2 52G
```

Re-pack the image to remove zeroed blocks:

qemu-img convert -O qcow2 vm-602-disk-0.qcow2 vm-602-disk-0-slim.qcow2

After conversion, the new QCOW2 file was only 30 – 35 GB instead of 2 TB.

7. Replace and Test

In the Proxmox web UI, detach the old QCOW2 disk.
Attach the new vm-602-disk-0-slim.qcow2.
Boot the VM and confirm that Windows 2003 loads and all services run normally.
Once verified, delete or archive the old file.

8. Results and Lessons Learned

Key takeaways:

The XP-compatible VMware vCenter Converter successfully performed the P2V migration.
Modern Windows tools can safely shrink old NTFS partitions when Clonezilla / GParted fail.
Clonezilla and GParted Live may misinterpret older NTFS metadata and falsely report corruption.
Running sdelete -z is essential for reclaiming space but extremely slow on IDE-based disks.
Combining sdelete + qemu-img convert provides a real, measurable disk-size reduction.

Final result

The original 2 TB disk image was reduced to a 52 GB virtual size and physically compressed to about 35 GB.
The system boots normally; IIS and internal applications work as before.
The only truly time-consuming step was SDelete, which required almost two weeks over IDE — using VirtIO would dramatically reduce that time.