iPhone Documents directory maximum size

I'm just wondering due to new personal project which开发者_开发技巧 is the limit (in MB or GB) of documents directory of my app. I just wanna save a lot of photos, so, has documents directory a limit for archiving downloaded photos? Will saving 300MB of photos produce slow downs on 3G? If there is no limit, I think that limit shoud be the 8 16 32 GB of the iPhone, are there any method to know the free space?

According to a discussions.apple.com: There is a limit of 2 GB.

https://discussions.apple.com/message/7599983?messageID=7599983#7599983?messageID=7599983

Files in the document directory stay there permanently until the app is removed.