To my understanding, the method is pretty straight-forward.
No vSphere server method (i.e. stand-alone):
- Manually grab config you need (IP address, any hardware-config details like VLAN, NTP configs if any) via vSphere client.
- Configure BIOS to boot from USB before HD.
- Boot to USB.
- Connect to the ESXi instance via vSphere client
- Add in the config grabbed in step 1 as appropriate
- Perform a Rescan Devices from Storage Adapters to locate any VMFS volumes.
- Browse the newly discovered Data Stores.
- When you find .vmx files, right click and select "Import into inventory"
vSphere method with vMotion:
- Migrate all VMs off of the ESXi server.
- Manually grab any special config you need (VLAN config being most important, NTP)
- In vSphere, Disconnect the host, then delete it.
- Configure BIOS to boot from USB before HD.
- Boot to USB.
- In vSphere, Add Host, and pick the hostname and login info for the USB-ESXi you created.
- Manually enter the config grabbed in step 2 as appropriate.
- Rescan your storage adapters for VMFS volumes.
- Migrate a VM to this server to make sure it works.
vSphere method without vMotion (uncommon, but could happen):
- Manually grab any special config you need (VLAN config being most important, NTP)
- Turn off all VMs on the machine.
- Follow steps 3-8 of the "with vMotion" checklist.
- Follow steps 7-8 of the "no vSphere" method.
Note: When you disconnect the host, associated VMs will go into 'Orphan'. It is possible that when you do the Rescan Devices they'll all come back and there will be no need to do step 4.