How to add additional data store SAN to esxi box
If you are looking to extend an existing datastore, the resolution steps mentioned in the below KB should help you.
VMware KB: Growing or expanding a VMFS volume or datastore
no, am looking for how to add additional storage to ESXi
I think, you mean to mount additional LUN to ESXi box so that you can add these LUNs as datastore on ESXi.
Please refer: https://www.youtube.com/watch?v=6XSabDgWob4.
Once the Storage(NFS/ISCSI/FC) is presented to your ESXi from the Storage level, you could follow the below steps in the KB to add the SAN to your esxi.
If still you are looking for something else, please elaborate your requirement.