The eZ Publish 5 API supports multiple binary file handling mechanisms by means of an IOHandler interface.
The Legacy IO Handler
The system comes with three handlers: Legacy, InMemory and Filesystem. Only Legacy is supported in eZ Publish 5.1. It uses the Legacy Kernel, that supports the DFS file handler, in order to provide clustering features for scalability and safety. This handler provides multi-server storage by means of a database + a network share.
Setup
No eZ Publish 5 level steps are required at the time of 5.1. See the legacy documentation page that explains how to setup a DFS cluster.
Configuration
YAML
No configuration is required on the new stack. The handler will reuse whatever configuration is defined in your eZ Publish Legacy instance. By default, Legacy will be configured to use the FS cluster handler, meaning files will be stored on the filesystem. No further configuration will be required.
The Legacy documentation explains how to enable clustering: http://doc.ez.no/eZ-Publish/Technical-manual/5.x/Features/Clustering.
Note that the only two supported options are now FS and DFS. The DB cluster is deprecated, and doesn't exist in eZ Publish 5.1.
Web server
As for legacy, rewrite rules are required in order to serve files stored in a DFS cluster. The virtualhost setup documentation provides the required rules.