Chose Enable.
The 5big confirms that UPnP/DLNA is now enabled. By default, everything in the Public folder is exposed to the UPnP server that is onboard. Re-indexing the database is accomplished by clicking the pencil icon next to UPnP/DLNA and choosing Reindex, as in this screen shot.
Video
I have a variety of videos on this device, including h.264 video/AAC3 audio encoded files in MP4 format and WTV formats.
Photos
My photo are all stored in JPG format, with nothing special about them.
Music
Music is all in M4A (iTunes) format.
I am able to play back all of my 1080i WTV files (recorded in Media Center) as well as all other MP4 videos on the unit; playback has been successful using the PlayStation 3, XBOX 360, Samsung Galaxy Tab 2 7.0, Samsung Galaxy S3 and a Sony Blu-Ray player with UPnP support with no issues. Likewise, all of my photo and music files were served up with no issues. I noticed one online review that saw issues with photos streaming only thumbnails from the 5big NAS Pro; I did not see that at all. I had zero issues with playback.
However, competing Linux-based NAS units are starting to offer transcoding abilities with like Atom-based units by allowing packages like Plex Media Server to be installed on them. Lacie does not have an equivalent manner for extending the NAS unit with add-on packages; if transcoding is a requirement, the Lacie solution will not work for you.
iTunes Server
Another core feature offered by equivalent NAS units is the ability to have the NAS serve as an iTunes server to support sharing and streaming of iTunes content inside the network to iTunes clients such as Apple TV’s and Mac computers. Lacie also offers this feature. Again, log onto the dashboard and you are greeted with this:

Hi Jim,
Thank you for the in depth review of the streaming capabilities of this NAS. I am considering the purchase of this particular model and I was wondering if it is capable of streaming video to an apple tv. I currently have a qnap 219P II and am looking to expand my storage.
Keep up the good work!
Hello, I saw that the manual of the Lacie 5big NAS Pro does not list the m4a format among the itunes server compatible formats. Did you had any issue streaming this format?