As if Gran Turismo 5 didn't take enough time in development, it seems the popular racing franchise is set on stealing more time - yours. And it is going to get it one way or another. 

Note that this installation is optional, and you may still do the basic 256 MB basic installation if you don't have space to spare. But if you do this, then expect to wait longer at loading screens every time you play. 

Or you can suck it up and wait the hour and use the 10 GB of space. In the long run you'll probably end up saving yourself time by doing this. 

Internet forum scrounger Amar212 received a PAL version of the game and reported that the installation warned that "install of game data can take up to 50 minutes." According to him, it took 40 minutes and used up 6.4 gigabytes, but learned that GT5 continued to unpack itself during playtime and took up even more space.