VMware ESXi and vSphere Cluster Management
What Is Virtual Machine Migration in VMware vSphere?
Learn what VM migration means in VMware vSphere and compare cold migration, suspended migration, vMotion, and Storage vMotion.
What Is Virtual Machine Migration?
A virtual machine (VM) is a software-defined computer that runs an operating system and applications. VM migration is the process of relocating that VM between an ESXi host, a datastore, or both.
An ESXi host is a physical server running the VMware ESXi hypervisor. A datastore is a storage container or location that holds VM files, such as virtual disks and configuration files.
Depending on the selected migration method, migration can change the VM's compute execution location, its VM file location, or both. Moving the compute location means running the VM on a different ESXi host. Moving the file location means placing the VM's files on a different datastore.
Why Migrate a VM?
Migration gives administrators flexibility when workloads need to move between physical hosts or storage locations. Common reasons include:
- Improving resource utilization: Distribute CPU, memory, and other demand more effectively across physical hosts.
- Balancing workloads: Move a busy VM away from an overutilized host to a host with more available capacity.
- Changing storage placement: Relocate VM files to another datastore when storage capacity or placement requirements change.
- Supporting operations: Move workloads to suitable hosts or datastores as infrastructure needs change.
Resource utilization describes how workloads consume and distribute available host resources. Workload balancing is the redistribution of VMs among hosts to improve that resource use.
Migration Choices by VM Power State
The VM's power state is one of the first factors to check. A VM may be powered off, suspended, or powered on. Each state is associated with different migration methods.
| Migration type | VM power state | What moves | Primary destination | Typical purpose |
|---|---|---|---|---|
| Cold migration | Powered off | The VM and, when selected, its compute placement and files | ESXi host, datastore, or both | Relocating a nonrunning VM |
| Suspended migration | Suspended | The suspended VM and, when selected, its compute placement and files | ESXi host, datastore, or both | Relocating a VM without leaving it actively running |
| vSphere vMotion | Powered on | The VM's active compute execution location | Another ESXi host | Host-to-host movement and resource balancing |
| vSphere Storage vMotion | Powered on | The VM's files | Another datastore | Changing storage placement while the VM remains running |
Cold Migration
Cold migration moves a VM while it is powered off. The VM is not running during the relocation. Depending on the selected destination, the operation can move the VM to another ESXi host, another datastore, or both.
For example, an administrator can move a powered-off test VM to a different host and datastore. Because the VM is not executing during the move, this is a nonrunning workload relocation.
Suspended VM Migration
Suspended migration relocates a VM while the VM is suspended. A suspended VM is not actively executing guest workloads, but its current execution state is retained so it can resume later.
Suspended is different from powered off: a powered-off VM has stopped running, while a suspended VM has paused its execution state. It is also different from powered on, where the guest operating system and applications are actively running.
vSphere vMotion
vSphere vMotion moves a powered-on VM from one ESXi host to another. Its primary purpose is host-to-host workload movement, such as balancing demand between physical servers.
For example, suppose one ESXi host is overutilized while another has available CPU and memory capacity. An administrator can use vMotion to move a running VM to the less-busy host. The destination is an ESXi host because the main change is where the VM executes.
vMotion should not be confused with Storage vMotion. vMotion primarily changes compute placement; Storage vMotion primarily changes VM file placement.
For related planning, review Enhanced vMotion Explained and CPU Compatibility for vMotion.
vSphere Storage vMotion
vSphere Storage vMotion moves the files of a powered-on VM from one datastore to another. The VM remains powered on while its storage location changes.
This operation changes the VM's file placement rather than its primary compute placement. For example, an administrator can move a running VM's files from a datastore with limited capacity to another datastore with more available space, while the VM continues running.
The destination in a Storage vMotion operation is a datastore. This differs from vMotion, whose primary destination is another ESXi host.
Host Destinations and Datastore Destinations
Migration destinations describe what aspect of placement is changing:
- ESXi host destination: Determines which physical server provides compute resources and runs the VM.
- Datastore destination: Determines where the VM's files are stored.
- Both: A migration of a powered-off or suspended VM can relocate compute placement and file placement together when those destinations are selected.
Keeping these destinations separate makes it easier to choose the correct migration method. If the problem is host resource demand, consider host migration such as vMotion for a powered-on VM. If the problem is storage capacity or placement, consider Storage vMotion for a powered-on VM.
Migration Concurrency for a VMFS5 Datastore
VMFS5 is version 5 of VMware's Virtual Machine File System. When multiple storage-related migrations target the same VMFS5 datastore, the supported limit is up to eight concurrent migrations to one VMFS5 datastore.
| Destination storage type | Supported concurrent migrations | Operational implication |
|---|---|---|
| Single VMFS5 datastore | Maximum of 8 concurrent migrations | Stage or queue additional migrations so no more than eight target that datastore at the same time |
This limit matters when planning several Storage vMotion or other storage-related moves into one VMFS5 destination. It is a scheduling constraint for the destination datastore, not a reason to stop all migration work.
Practical Migration Examples
Balancing an overutilized host
A running VM is consuming resources on an overutilized ESXi host. Another host has more available capacity. The administrator uses vMotion to move the powered-on VM to the other host, changing its compute execution location.
Moving storage without powering off the VM
A running VM's files are on a datastore that needs to be cleared or has insufficient capacity. The administrator uses Storage vMotion to move the files to another datastore while the VM remains powered on.
Relocating a nonrunning VM
A powered-off VM needs to be placed on another host or datastore. The administrator uses cold migration. Because the VM is powered off, it is not running during the relocation.
Planning several storage moves
An administrator schedules multiple migrations to the same VMFS5 datastore. The administrator allows no more than eight simultaneous incoming migrations to that datastore and queues the remaining work.
How to Select the Migration Type
- Check whether the VM is powered off, suspended, or powered on.
- Decide whether compute placement, VM file placement, or both must change.
- Choose cold migration for a powered-off VM, suspended migration for a suspended VM, vMotion for powered-on host movement, or Storage vMotion for powered-on datastore movement.
- When targeting a VMFS5 datastore, schedule storage migrations so no more than eight target that datastore concurrently.
Troubleshooting Migration Selection
More than eight migrations target one VMFS5 datastore
Symptom: More than eight migrations are planned to the same VMFS5 datastore at once.
Likely cause: The destination datastore has a supported concurrent migration limit.
Resolution: Stage or queue the migrations so no more than eight simultaneously target that VMFS5 datastore.
The migration type does not match the VM state or destination
Symptom: The selected migration method does not fit the VM's current power state or the intended destination.
Likely cause: Host migration, storage migration, and powered-off or suspended migration have been confused.
Resolution: Confirm whether the VM is powered off, suspended, or powered on. Then select cold migration, suspended migration, vMotion, or Storage vMotion according to the required host or datastore destination.
Exam-Ready Summary
- VM migration relocates a VM between ESXi hosts, datastores, or both.
- Cold migration applies to a powered-off VM.
- Suspended migration applies to a suspended VM.
- vMotion moves a powered-on VM to another ESXi host.
- Storage vMotion moves a powered-on VM's files to another datastore.
- An ESXi host is the compute destination; a datastore is the VM file destination.
- Up to eight concurrent migrations are supported to one VMFS5 datastore.
For foundational context, see the VMware ESXi Online Course, Create Virtual Machines, and Browse VMFS Datastores lessons.