I had quite an interesting case recently where I had to build stretch cluster for a customer using Oracle GI 12.1 and placing quorum voting disk on NFS. There is a document at OTN regarding the stretch clusters and using NFS as a third location for voting disk but it has information for 11.2 only as of the moment. Assuming there is no difference in the NFS parameters I used the Linux parameters from that document and mounted the NFS share on the cluster nodes.
Later on when I tried to add the third voting disk within the ASM disk group I got this strange error:
SQL> ALTER DISKGROUP OCRVOTE ADD QUORUM DISK '/vote_nfs/vote_3rd' SIZE 10000M /* ASMCA */ Thu Nov 14 11:33:55 2013 NOTE: GroupBlock outside rolling migration privileged region Thu Nov 14 11:33:55 2013 Errors in file /install/app/oracle/diag/asm/+asm/+ASM1/trace /+ASM1_rbal_26408.trc: ORA-17503: ksfdopn:3 Failed to open file /vote_nfs/vote_3rd ORA-17500: ODM err:Operation not permitted Thu Nov 14 11:33:55 2013 Errors in file /install/app/oracle/diag/asm/+asm/+ASM1/trace /+ASM1_ora_33427.trc: ORA-17503: ksfdopn:3 Failed to open file /vote_nfs/vote_3rd ORA-17500: ODM err:Operation not permitted NOTE: Assigning number (1,3) to disk (/vote_nfs/vote_3rd) NOTE: requesting all-instance membership refresh for group=1 Thu Nov 14 11:33:55 2013 ORA-15025: could not open disk "/vote_nfs/vote_3rd" ORA-17503: ksfdopn:3 Failed to open file /vote_nfs/vote_3rd ORA-17500: ODM err:Operation not permitted WARNING: Read Failed. group:1 disk:3 AU:0 offset:0 size:4096 path:Unknown disk incarnation:0xeada1488 asynchronous result:'I/O error' subsys:Unknown library krq:0x7f715f012d50 bufp:0x7f715e95d600 osderr1:0x0 osderr2:0x0 IO elapsed time: 0 usec Time waited on I/O: 0 usec NOTE: Disk OCRVOTE_0003 in mode 0x7f marked for de-assignment Errors in file /install/app/oracle/diag/asm/+asm/+ASM1/trace /+ASM1_ora_33427.trc (incident=83441): ORA-00600: internal error code, arguments: [kfgscRevalidate_1], , , , , , , , , , ,  ORA-15080: synchronous I/O operation failed to read block 0 of disk 3 in disk group OCRVOTE
This happens because with 12c direct NFS is used by default and it will use ports above 1024 to initiate connections. On the other hand there is a default option on the NFS server – secure which will require any incoming connections from ports below 1024:
secure This option requires that requests originate on an internet port less than IPPORT_RESERVED (1024). This option is on by default. To turn it off, specify insecure.
The solution for that is to add insecure parameters to the exporting NFS server, remount the NFS share and then retry the above operation.
For more information refer to:
12c GI Installation with ASM on NFS Disks Fails with ORA-15018 ORA-15072 ORA-15080 (Doc ID 1555356.1)