Why is the OCR&Vote disk group servicing SCAN name
That is the Oracle Cluster Registry (OCR) where information about clusterware components is stored.

http://docs.oracle.com/cd/E11882_01/rac.112/e41959/intro.htm#CWADD90952

Its size is 256 MB, or 0.26GB, you can check this with ocrcheck:

# ocrcheck
Status of Oracle Cluster Registry is as follows :
         Version                  :          3
         Total space (kbytes)     :     262120
         Used space (kbytes)      :       2948
         Available space (kbytes) :     259172
         ID                       : 1703252243
         Device/File Name         :       +OCR
                                    Device/File integrity check succeeded

                                    Device/File not configured

                                    Device/File not configured

                                    Device/File not configured

                                    Device/File not configured

         Cluster registry integrity check succeeded

         Logical corruption check succeeded