@sujay: your HDD will be added as a folder into the SSD. so you get the same read/write speeds as your SSD when you add data into that folder. in reality the data will be in the HDD but the IO speed will be of SSD.
Its not really unlimited but depends on the size of your HDD.
Thats fantastic if it works. But it also put a question why would one buy SSD's of larger capacity if such things can be possible?