HCX Bulk or RAV migration is stuck at 0% Base sync for a Virtual Machine

Products

• VMware HCX
• VMware vSphere ESXi

Issue/Introduction

• HCX bulk migration/RAV does not progress for one particular VM.
  
  
• The initial base synchronization remains at 0%, as confirmed in the HCX Manager(Connector or Cloud) logs located at /common/logs/admin/app.log
[YYYY-MM-DDTHH:MM:SS] UTC [ReplicationTransferService_SvcThread-3515, Ent: HybridityAdmin, , TxId: TxId: <Transaction ID of the migration> WARN  c.v.h.s.r.j.ReplicationTransferMonitor- Current bytes transferred value 0 is not greater than the already transferred bytes value 0, hence not updating for transfer <UUID of migration ID>
  
  
• On the ESXi where the VM resides you would see this log message under /var/run/log/vmkernel log:
  [YYYY-MM-DDTHH:MM:SS] cpu24:311746948)WARNING: Hbr: 4813: Failed to establish connection to [x.x.x.x]:31031(groupID=VRID-########-####-####-####-###########): Corrupt response from replication server
  
  
• The affected VM has more than 64 disks attached.

Environment

• VMware HCX
• VMware vSphere 8.x

Cause

HCX Bulk and RAV migrations utilize the vSphere Replication engine for the initial base sync. In VMware ESXi 8.0 and earlier versions, the maximum number of protected disks per virtual machine is hard-limited to 64. When a VM exceeds this limit, the replication server cannot process the request, leading to the "corrupt response" connection failure and halting the migration at 0%.

Reference - Operational Limits of vSphere Replication

Resolution

To resolve this issue, apply one of the following solutions depending on your environment's capabilities:

Option 1: Upgrade the Source Environment (Recommended for long-term)

• Upgrade the source ESXi hosts to version 8.0 U1 or higher.
• Note: Starting in ESXi 8.0 U1, the vSphere Replication limit for disks per VM was increased, allowing HCX to process VMs with up to 255 disks.

Option 2: Reduce VM Disks (Immediate Workaround)

• Cancel the stalled migration task for the affected VM in the HCX Manager UI.
• Consolidate or remove disks on the source VM to reduce the total number of attached virtual disks to 64 or fewer.
• Once the disk count is 64 or below, re-initiate the HCX Bulk or RAV migration task.

Additional Information

Note: If your Virtual Machine has 64 or fewer disks and is still stuck at 0% Base Sync, this may be caused by a network routing, MTU, or port block issue between the ESXi host and the HCX-IX appliance.

Please refer to: HCX Bulk and RAV Migrations Stalled at 0% Base Sync