deviceの切り離しは、こんな感じのようだ
[root@localhost 000]# mogadm device list
localhost [1]: alive
used(G) free(G) total(G)
dev1: alive 1.729 5.046 6.774
dev2: alive 1.729 5.046 6.774
dev3: alive 1.729 5.046 6.774
[root@localhost 000]#mogadm device mark localhost dev3 dead
localhost [1]: alive
used(G) free(G) total(G)
dev1: alive 1.729 5.046 6.774
dev2: alive 1.729 5.046 6.774