A synchronization protocol for multi-premises hosting of digital content items. In one embodiment, for example, a method comprises the operations of: detecting creation or modification of a content item; determining a content item namespace to which the content item belongs; obtaining a plurality of identifiers of a plurality of block servers to which the content item namespace is assigned; making a selection of one of the plurality of block servers as a target block server; and uploading any content item blocks of the content item to the target block server that are not already stored at the target block server.