US. Patent Mar. 6, 2012 Sheet 1 015 US 8,131,960 B2 8 18b 1 [1 36 Off 0 l / 0 Off Host 1 O\ 0 Storage 1 Host2 O \O Host (n\ O Off 0 Storage I O /O Storage2 Storage (n) O O O//O Storage2 Storage (n) n (m 8/ 0 Host 1 O Host2 0 Host (m