http://utcc.utoronto.ca/~cks/space/blog/solaris/ZFSHowMetadataUpdates
http://utcc.utoronto.ca/~cks/space/blog/solaris/ZFSRewriteDesire
http://utcc.utoronto.ca/~cks/space/blog/solaris/ZFSUberblockWrites
http://www.osdevcon.org/2009/slides/zfs_internals_uli_graef.pdf