Milkman,
Like your name, your description indicates something that is fairly healthy. A thin volume will only account for the blocks that are used. The fully zeroed LUN is reporting the used blocks back to the volume. If you have "Snapshot Thin Provisioning" configured (i.e. snap autodelete AND autogrow, as mentioned above) then here is what happens:
First snapshot freezes all of the used blocks in the volume (the entire LUN). When new writes occur, space in the volume will be consumed to provide space for those writes (this is why the snap reserve is irrelevant in this config; *all* of the space is meant for redirected writes after snaps [unless one does the sacrilege of adding other data to this volume--set it to 0).
As additional snaps continue to freeze blocks, the remaining space in the volume will continue to be consumed for new writes. At a particular percentage threshold (~above 85%; adjustable), snap autodelete will begin removing snapshots to free up blocks that were previously frozen. Autogrow is important: once a percentage threshold is crossed, this will automatically grow the volume to provide additional blocks to be used for new writes.
A thin volume, in this scenario, makes all the blocks discussed (i.e. all that are not in the original frozen LUN) available to the aggregate to offer to other volumes. Once you get to the point where you are exhausting the supply and growing the volume, the thin thing makes no difference.
Does this sour you... or make you shake? : )
