Chunk map/control

[Phillip Susi <psusi@cfl.rr.com>]

Is there currently a way to view and manipulate the chunks?  If I
understand things correctly, a new fs has a few chunks:

1)  System chunk.  Contains tree of trees, device tree, chunk tree.
2)  Metadata chunk.  Contains the directory tree for the default subvol,
and any additional subvols/snapshots you create.  Directory entries and
inodes are in this tree.
3)  Data chunk.  Files with significant data have blocks allocated from
this chunk.

The system chunk is always mirrored, even on a single disk.  The
metadata chunk is mirrored by default, but can be changed with a
parameter to mkfs.  The data chunk is striped by default, but can be
changed via parameter to mkfs.  The chunks are all expanded as needed.
Is this correct, and is there a way to create a subvol with a new pair
of metadata/data chunks and specify how they should be striped or
mirrored across what devices?