OS Assisted Migration (OSAM) Initial Sync Failed: Transfer Error (JSON object 'mbrPartitions' not found)

Products

• VMware HCX

Issue/Introduction

During an OS Assisted Migration (OSAM) from a KVM source to a VMware destination, the initial sync fails during the transfer phase. The HCX Manager display shows a generic transfer error, while the Sentinel logs or detailed job status reveal the following error messages:

• JSON object 'mbrPartitions' not found.

 

Initial Sync Failed:

Transfer Error (JSON object 'mbrPartitions' not found.)

Environment

• Product: VMware HCX
• HCX Version: 4.11.4 (and potentially earlier)
• Source Environment: KVM
• Guest OS: Red Hat Enterprise Linux (RHEL) 8.x / 9.x
• Disk Configuration: LVM Physical Volumes (PV) created directly on raw disks (e.g., /dev/sdf) without a partition table (MBR or GPT).

Cause

The VMware HCX Sentinel agent requires a standard partition table (MBR or GPT) on all attached block devices to build the replication blueprint. When a disk is configured as a "whole-disk" LVM member (where the LVM PV is created on the raw device like /dev/sdX rather than a partition like /dev/sdX1), the Sentinel agent cannot find a partition table. This causes the agent to return a null value for the mbrPartitions array, leading to a malformed JSON payload and a fatal NullPointerException during the migration transfer.

Resolution

To resolve this issue, you must ensure that all disks slated for migration have a standard partition table.

1. Log in to the source VM and identify disks without partitions using the following command: lsblk -f
2. Review the output for disks that show an LVM2_member directly on the device name (e.g., sdf) without a numeric partition suffix (e.g., sdx1).
3. For any disk identified with a whole-disk configuration, you must either:
   • Modify the Disk: Re-provision the storage to include a standard MBR or GPT partition table and move the LVM Physical Volume to a partition (e.g., ####/sdx1).
   • Remove the Disk: If the disk is not required for the migration, detach it from the source VM.

Additional Information

For RHEL workloads, standard partitioning practices (creating /dev/sdX1) are mandatory for compatibility with the HCX OSAM framework.