Not able to mount the diskgroup. getting error as follows

Thu Aug 27 07:52:29 2015

SQL> alter diskgroup DATA mount

NOTE: cache registered group DATA number=35 incarn=0x695fe4d4

NOTE: cache began mount (first) of group DATA number=35 incarn=0x695fe4d4

NOTE: Assigning number (35,12) to disk (ORCL:V_6303_1D12)

NOTE: Assigning number (35,13) to disk (ORCL:V_6303_1D13)

NOTE: Assigning number (35,7) to disk (ORCL:V_6303_1D2B)

NOTE: Assigning number (35,8) to disk (ORCL:V_6303_1D2C)

NOTE: Assigning number (35,9) to disk (ORCL:V_6303_1D2D)

NOTE: Assigning number (35,10) to disk (ORCL:V_6303_1D2E)

NOTE: Assigning number (35,11) to disk (ORCL:V_6303_1D2F)

Thu Aug 27 07:52:29 2015

ERROR: no PST quorum in group: required 1, found 0