I think this document has a significant error.
In chapter 3.2 VOLUME AND AGGREGATE SETUP AND OPTIONS -> BEST PRACTICES FOR CONTROL AND LOG Fils:
"Create a minimum of two online redo log groups, each with three members. Put the first online redo log group on one volume and the next on another volume."
If you follow this recommendation, the loss of a one volume where all members of the redo log group, Oracle can not write to this redo online group.
If you make the two and more redo log groups, each with two members, and the first member of each redo log groups put on a first volume, the second member of each redo log group to second volume, oracle will write to redo log even if you lost any of volume with online redo logs.
For a more complete understanding read the following documentation:
http://docs.oracle.com/cd/E11882_01/server.112/e10897/storage.htm#CACDFFGG
http://docs.oracle.com/cd/E11882_01/server.112/e25789/physical.htm#i1006163
Am I right or wrong?