Dropbox, Inc.
Storage constrained synchronization engine

Abstract:

A content management system synchronizes content items across client computing systems connected by a network. If a storage allocation for shared content items on a client device is exceeded by the request to add or edit a content item such that it is enlarged, a client application or the host of content management system selects content items to remove from residence on the client device but keep remotely on content management system. Upon removal of the selected content items, the client application creates shadow items, representing the content item but only containing the metadata of the content item. This creates sufficient space while maintaining user access to all synchronized shared content items. Entries in a file journal may be used to track and manage whether a stored item is a content item or a shadow item.