Microsoft Surface Pro mSATA SSD Upgrade: Dangerous but Successful
 

Unlike current ARM or Atom based tablets, Microsoft's Surface Pro integrates a full blown mSATA SSD. My review sample included a 128GB Micron C400, while I've seen reports of users getting Samsung PM830 (OEM SSD 830) based drives. Both of these drive options are great so long as you remember to keep a good amount of space on the drive free (15 - 25% free space is a good rule of thumb). Unfortunately, Microsoft only offers two capacities (64GB and 128GB) despite there being much larger mSATA SSDs available on the market. To make matters worse, supplies have been tight of the 128GB Surface Pro, with 64GB models a little easier to come by.

A few adventurous Surface Pro owners have decided to try to swap out their 64GB mSATA SSDs with larger models. One of our readers (Tim K.) managed to successfully transplant a 240GB Intel SSD 525 in his Surface Pro. The trick is to make sure you clone the original GPT formatted mSATA SSD properly. For this, Tim used Reflect to clone the drive and MiniTool Partition Wizard to expand the data partition to the full capacity of the new SSD.

http://www.anandtech.com/show/6756/m...but-successful