Windows Dynamic Disk (LDM) migration issue

Problem Statement

We are encountering failures when attempting to migrate Windows VMs with dynamic disks (LDM - Logical Disk Manager) from VMware to KVM through VJailbreak’s migration pipeline. VJailbreak uses virt-v2v internally for VM conversion, and the migration fails during the virt-v2v inspection phase with Hivex-related errors when attempting to read Windows registry hives.

VJailbreak Context

VJailbreak The migration workflow involves:

1. Migration Trigger: User creates a Migration specifying source VMs
2. Migration Controller: VJailbreak controller reconciles the Migration
3. Virt-v2v Execution: Controller spawns virt-v2v pods to perform the actual conversion
4. Conversion Phase: Virt-v2v converts VMware disk formats and installs KVM drivers
5. Import Phase: Converted VMs are imported into the target KVM environment

The LDM issue manifests during step 3-4, where virt-v2v fails to inspect and convert Windows VMs with dynamic disks.

Technical Background

What is LDM?

• LDM (Logical Disk Manager) is Windows’ proprietary volume management system for “dynamic disks”
• Similar in concept to Linux LVM, but incompatible with standard partition tables
• Stores volume metadata in a 1MB journaled database at the end of each disk
• Commonly used for spanning volumes across multiple disks, mirroring, or RAID configurations

How Virt-v2v Works

1. Inspection Phase: Uses libguestfs APIs to detect OS, read registry hives via Hivex
2. Mounting: Mounts filesystems based on inspection data
3. Conversion: Installs VirtIO drivers, removes old hypervisor drivers, modifies registry
4. Registry Operations: Requires both read and write access to SYSTEM and SOFTWARE hives

Root Cause Analysis

Why LDM Causes Failures

Inspection Dependency Chain:

VJailbreak MigrationTrigger Controller
  └─> Virt-v2v Pod
      └─> libguestfs inspection
          └─> Hivex library (registry reading)
              └─> Direct file access to registry hives
                  └─> FAILS if hives are on LDM volumes

Linux LDM Support Limitations

1. LDM volumes may not be properly assembled by libguestfs
2. Registry hives may be fragmented across LDM volumes
3. Hivex expects complete, contiguous registry files
4. Even if volumes assemble, registry data may appear corrupted

Impact on VJailbreak Migration Workflow

Recommended Solutions

Solution 1: Pre-Migration Disk Conversion (RECOMMENDED)

Steps:

1. Before creating Migration, boot Windows VM in VMware vSphere

2. Disable Fast Startup:

   powercfg /h off

3. Convert dynamic disks to basic:

   diskpart
   list disk
   select disk 1
   convert basic
   select disk 2
   convert basic

4. Clean shutdown: shutdown /s /f /t 0

5. Do the migration in vJailbreak

Note: convert basic requires empty disk. If data exists, must backup → clean → convert → restore.

In VJailbreak: Retry the migration

Impact on Non-Root Disks

Important: Virt-v2v only inspects the root/boot disk where Windows is installed.

Configuration	Result	Action
Root: Basic, Data: LDM	Works	Import LDM disks in Windows post-migration
Root: LDM, Data: Basic	Fails	Must convert root disk to basic
Root: LDM, Data: LDM	Fails	Must convert root disk (data optional)
All: Basic	Works	No action needed

Conclusion

Primary Recommendation for VJailbreak Users: Before creating MigrationPlans for Windows VMs, verify disk configuration in VMware vSphere. If dynamic disks are detected, boot the VM, disable Fast Startup, convert dynamic disks to basic using diskpart, perform a clean shutdown, then proceed with VJailbreak migration.