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There are two supported methods for migrating a VM from a VMFS datastore on a SCSI presented device to an NVMe presented device: online and offline.
The online method uses VMware Storage vMotion to move the VM between protocols. This method requires two devices, the SCSI VMFS datastore where the VM resides, and a new, NVMe presented device with a new VMFS datastore.
The offline method entails resignaturing the VMFS datastore after presenting it over the new NVMe protocol. Recall that the signature of a VMFS datastore partially consists of the device ID. Since SCSI and NVMe present different formats for the ID, VMware shows a mismatch when the device is presented through a different protocol. Therefore, the device must be resignatured, and the VMs re-registered.
Each method has its pros and cons. The online method allows no downtime, yet double the storage is used (at least initially), and it can be time consuming. The offline method is fast, however it does require downtime, no matter how short. A customer should weigh these pros and cons to come up with a suitable plan for migration. For small environments, Storage vMotion may be perfectly acceptable. However, large environments may require using both methods, determining which datastores must remain online and which ones can suffer downtime.
Dell, together with VMware, validated the offline method in the KB SCSI to NVMe VMware VMFS Datastore Offline Migration Steps.