PowerScale Data Protection - Protection Level 2x - What does it mean / What is it for?

Hi all, 

I am wondering what the protection level of 2x means, compared to 3n:1d for instance.

The description in various documents just states "Mirrored over 2 [to 8] nodes, depending on configuration", but it is not clear what is mirrored exactly, which configuration is possible, or what failure the protection level tolerates. 
Does it refer only to metadata, as the following paragraph seems to suggest? - "OneFS also provides various mirroring options ranging from 2x to 8x, allowing from two to eight mirrors of the specified content. Metadata, for example, is mirrored at one level above FEC by default. For example, if a file is protected at +1n, its associated  metadata object will be 3x mirrored."

I am told that this is not a mirror of actual user data and therefore would not tolerate the loss of half the nodes. Can somebody confirm and shed some light on this protection level?

Thanks,
Georg