SaaS Web app storage

[eluser]CI Freak[/eluser]
I'm just wondering whats the best way to do this, im writing an application which will run on the rackspace cloud, there will be only one copy of code running between all users. What's the best way to store the users files?

I want to keep them out of the htdocs folder, and all users will have an identical set of upload directories

eg.

/user1_uploads/files/
/user1_uploads/images/
/user1_uploads/documents/

/user2_uploads/files/
/user3_uploads/images/
/user4_uploads/documents/

i want to keep everything on the one server as it will scale itself automatically, but i also need to make sure user1's instance cant access user2's files.

[eluser]ankur0101[/eluser]
Using PHP, you need to create directory which would be same as username i.e. user1_upload. You need to provide full path in PHP code to create directory.
Make use of mysql. Store all names of files in mysql. While fetching or downloading, do authentication.