This could be a little bit off-topic, but I found something called Haystack (from Facebook) and MObStor (from Yahoo), it seems to me they are more suitable to my project.
 
http://www.facebook.com/note.php?note_id=76191543919&ref=mf
http://developer.yahoo.net/blog/archives/2009/07/mobstor.html

CB
2010/3/2 Jonathan Ellis <jbellis@gmail.com>
On Tue, Mar 2, 2010 at 11:57 PM, Cool BSD <cool@coolbsd.com> wrote:
> Be short - what's the ideal column size in real world?
>
> Long description - I'm working on a prototype, the application is a data
> store that holding blobs sizing from couple of KB to hundreds of MB, close
> to 1GB in the worst case.

You should be fine.  "Single digits of MB" is a good rule of thumb.