/vmfs/devices and /vmfs/volumes are VMware's way of grafting in the VMFS disk and fileystems to the service console. Generally you will only deal with /vmfs/volumes since that is where the VMFS filesystems are mounted.
BTW: I believe it is best practice to not create VMFS volumes intended for VM storage during installation. It is best to do that via the VI client. The VI client/Virtual Center do a little bit of extra work to make sure the disk alignment is optimal.
http://wannemacher.us
