Knowledge Base

vMotion

• Files for a virtual machine are not relocated when it is migrated using vMotion.
• The virtual machine is re-registered to the destination host.
• Any RDMs remain as RDMs when the virtual machine is registered to another host. That is, no changes to the virtual machine itself are made.

Cold migration

• Any non-RDM virtual disks are physically moved to the destination.
• The virtual machine configuration files are physically moved to the destination.
• Raw LUNs themselves cannot be moved, as they are raw disks presented from the SAN. However, the pointer files (RDMs) can be relocated if required.
• When performing a cold migration of a virtual machine with RDMs attached to it, the contents of the raw LUN mapped by the RDM are copied into a new .vmdk file at the destination, effectively converting or cloning a raw LUN into a virtual disk. This also applies when the virtual machine is not moving between ESX hosts. In this process, your original raw LUN is left intact. However, the virtual machine no longer reads or writes to it. Instead, the newly-created virtual disk is used.
• If you wish to cold migrate a virtual machine without cloning or converting its RDMs, remove them from the configuration of the virtual machine before migrating. You can delete the RDM from the disk when removing it (the raw LUN contents are not changed). Re-add them to the configuration when completed.
• For ESXi 5.x: During the migration you can use the advanced section of the migration wizard and select if you would like to maintain the same format of the files at the destination or convert it to a thick/thin disk.
• The virtual machine registration changes, but the files are left untouched.

Cloning

Storage vMotion

• When you perform Storage vMotion, the virtual machine files are physically relocated to a destination datastore. The same host retains ownership or registration of the virtual machine after Storage vMotion completes.
• For Virtual Infrastructure 3.5, virtual disks and virtual and physical mode RDM pointer files can be relocated to the destination datastore but cannot be converted to thick-provisioned or thin-provisioned disks during migration. The RDM pointer files of the virtual machine remain as RDM pointer files when the process completes.
• For vSphere 4.0 and higher:
  
  
  • Virtual disks and virtual mode RDM pointer files can be relocated to the destination datastore.
  • Virtual disks can be converted to thick-provisioned or thin-provisioned disks during migration as long as the destination is not an NFS datastore.
  • Physical mode RDM pointer files can be relocated to the destination datastore, but physical mode RDM data cannot be migrated to a VMDK disk using Storage vMotion.
    
  • Virtual mode RDM data can be migrated to a VMDK disk with Storage vMotion, provided sufficient licensing is present.
    

• In ESXi 5.0, during the Storage vMotion operation, virtual mode RDM data can be migrated to new VMDK disks by selecting either thick or thin provisioning for the disk type under the Advanced section of the migration wizard. Physical mode RDM data can be migrated to VMDK disks only via cold migration. For more information, see the Migrating RDMs, and a question for RDM Users blog post.
• If you do not change the destination format to thick or thin provisioned for an RDM in the advanced section of the migration wizard, only the RDM mapping file will be migrated to the destination datastore.
  
• If using N-Port ID Virtualization (NPIV), Storage vMotion is not supported. For more information, see the NPIV Capabilities and Limitations document.
• If you are attempting a Storage vMotion of a virtual mode RDM using the Advanced method, and the RDM pointer mapping file is already present in the target datastore, the Storage vMotion finishes quickly, but without moving the data. This is because the Storage vMotion detects that the source and target datastores for the mapping file are the same, and therefore concludes that no movement is needed.
  
  To work around this issue:
  
  1. Remove the RDM from the virtual machine, and delete it from disk to ensure the mapping file is deleted. This will not delete the data in the RDM.
  2. Add the RDM again, and put the mapping file in a different datastore than the ultimate target of the Storage vMotion.
  3. After the virtual machine reconfiguration is complete, attempt the Storage vMotion again.
     
     Note: To avoid downtime, you can migrate the virtual mode RDM pointer file to an alternate datastore (that is, any other datastore than the actual destination datastore), then Storage vMotion the same pointer file back using either Thick Zeroed or Thick Eager Zeroed disk format. Using the du -ah command, you can confirm if the pointer exists in the directory on the alternate datastore.

• Storage vMotion of virtual machines using virtual compatibility mode RDMs is supported, however clustered applications or clustered virtual machine configurations do not support Storage vMotion.
• RDM .vmdk pointer files must reside on VMFS datastores. The NFS protocol does not support SCSI commands. For more information, see Unable to add a physical mode disk mapping (RDM) to a virtual machine stored on an NFS datastore (1001856).

• Storage vMotion Remote Command-Line Syntax in the Basic System Administration Guide for your version of VMware ESXi/ESX.
• The vSphere Command-Line Interface Documentation.