For the uninformed, the game data is required for the Metal Gear Online multiplayer mode of Metal Gear Solid V: The Phantom Pain. With that said, you will also need to have the latest patch from the main game as well. The new title update is expected to arrive before the launch of Metal Gear Online on October 6th on the PlayStation 4, Xbox One, Xbox 360 and PlayStation 3 consoles (PC gamers will have to wait until early 2016 to gain access).
Similar to the situation with Grand Theft Auto Online and Grand Theft Auto V, Konami decided to release the main campaign of Metal Gear Solid V: The Phantom Pain first without the standard multiplayer mode. For Metal Gear Online, it looks like company is going to spilt the download between the upcoming patch in addition to the aforementioned Game Data Version 1.00 on the PlayStation Store.
The Phantom Pain was released last month on the 1st of September.
If you need more space for MGO, you can replace the internal HDD of the PS4 with one that has a bigger storage capacity. We suggest getting the OWC DIY 2.0TB Drive Upgrade Bundle if you are planning to do so. You can buy the kit with this link from Amazon.