Since Feeds 7.x-2.0-beta4, content downloaded via HTTP is cached on the file system (see change record). The directory to save the cached files in is configurable. By default, the cache directory is 'private://feeds/cache' (or 'public://feeds/cache' if you haven't a private file system configured).
You can override this variable by adding the following line to settings.php:
$conf['feeds_http_file_cache_dir'] = 'private://feeds/cache';
Unrecognized files in the cache directory will be deleted!
Important to know is that this directory should only be used for cached files. This is because Feeds regularly checks this directory for orphaned cache files. As explained in the change record Downloaded content is now cached on the file system, the headers of HTTP downloaded content are still saved in the database and the cache records in the database need to be kept in sync with the files in the cache directory. Any file in this directory that does not have a matching row in the database will be deleted periodically.
By default, Feeds will check each six hours for orphaned files in the cache directory. This interval can be changed by setting the 'feeds_sync_cache_feeds_http_interval' variable.
