Bulk migration uses the host-based replication to relocate a virtual machine between HCX data centers.
To reduce the downtime, the source VM remains online during the replication and is bootstrapped on the destination ESX host after replication completes.
A Bulk Migration request triggers the following actions:
Replication begins an initial full synchronization transfer to the remote site. The time it takes to replicate is a function of the size of the VM, the data change rate on the virtual machine disk files (VMDKs), and available bandwidth.
Replication bandwidth consumption varies depending on the number of disks for each VM and the number of VMs being migrated concurrently.
The switchover can start immediately after the initial synchronization is completed, or it can be delayed until a specific time using the scheduled migration option. By using the scheduled migration option, the switchover can occur during a maintenance window.
A delta synchronization with two-hour recovery point objective (RPO) occurs while waiting for the scheduled switchover, after the initial synchronization is completed.
- Depending upon data churn on source disk, additional snapshots are being created during the RPO cycle. After each RPO cycle, disk consolidation takes place and creates a “hbrdisk.RDID vmdk” called as replica instance vmdk file on target datastore. Refer VMware KB 87028.
During switchover, the source VM is powered-off to perform a final off-line synchronization, data consolidation, and VM instantiation at the target data center.
Following the switchover, the migrated VM replica is powered-on and HCX Manager renames the original VM using a POSIX timestamp suffix to avoid a naming conflict with the migrated VM. If the Retain MAC option was not selected, the migrated VM obtains a new MAC address.
- The migration completes and the original VM is copied to the Migrated VMs folder.
VMware HCX copies the original VM to the Migrated VMs folder. This copy can be accessed in the vSphere Virtual Machines and Templates view, and can be used to recover the migrated VM.
Single vCenter Operation
Requirements for Bulk Migration
The Hybrid Interconnect Service and the Bulk Migration Service must be activated and in a healthy state in the relevant service mesh.
- The resources to create, power on and use the virtual machine must be available in the destination environment.
- Virtual machines must be running Hardware Version 7 or later.
- Virtual machines must have VMware Tools installed.
- Virtual machines must reside in a Service Cluster (defined in the Compute Profile).
- Network Extension is required for low downtime migration operations.
- Personalization Scripts and System Identity changes (Hostname, IP, SID) require the system to be rebooted one additional time during the switchover phase.
- Bulk Migration potential throughput can vary depending on bandwidth available for migrations, latency, available CPU/MEM/IOPS, and disk read speed. For a successful switchover phase, the bandwidth and the network conditions must be sufficient to satisfy the operation considering the dataset and virtual machine data change rate. For more information about how to determine bandwidth requirements, see Bandwidth Requirements for vSphere Replication.
For information regarding the migration limits, see VMware Configurations Maximums.
Restrictions for Bulk Migration
Virtual machines with Raw Device Mappings (RDM) in Physical Compatibility mode cannot be migrated. Virtual machines with RDM in Virtual Compatibility mode can be migrated. They are converted to VMDKs at the destination.
Virtual machines with mounted ISO images cannot be migrated. The HCX Bulk migration operation can be used for force unmount ISO images.
Virtual machine snapshots are not migrated. The HCX Bulk migration operation has an option to remove the snapshots.
Virtual machines with DirectPath I/O configurations cannot be migrated without first removing the DirectPath device.
Virtual machines cannot be migrated while they are using a shared SCSI bus, flagged for multi-writer, enabled for fault tolerance, or configured for shared VMDK disk sharing.
Virtual machines that cannot be gracefully powered off cannot be migrated. HCX can override with the Force Power-off VM option.
Virtual machines using virtual NVMe (vNVME) Controllers cannot be migrated.
- Migration to or from vVOL datastores is not supported.
- The HCX Migration interface does not display port groups that are VLAN trunks.
If either the source or the destination vCenter version is earlier than 6.0, VMware vCenter tags attached to a virtual machine are not retained during migration. Tags can be created manually for those virtual machines after migration.
VMware software appliances (including, but not limited to vCenter Server and NSX Manager) cannot be migrated with HCX Bulk migration.
- vSphere VM Encryption is not supported with HCX migrations.
- Virtual Based Security (VBS) functionality is not supported with VMware HCX migrations.