I''ve put together some thoughts on the ZFS copies property. http://blogs.sun.com/relling/entry/zfs_copies_and_data_protection I hope that you might find this useful. I tried to use simplified drawings to illustrate the important points. Feedback appreciated. There is more work to be done to understand all of the implications presented by the copies feature, so if you find something confusion or have questions, then please speak up and I''ll add it to the list of things to do. I''ve already got performance characterization and modeling on the list :-) -- richard