Troubleshooting ORA-31693 ORA-31617 ORA-19505 ORA-27037 when expdp with parallel on RAC 11G

we introduced exporting in parallel to multiple files for spend up , but throw some error. my db and rac ars 11.2.0.3.
#cat dmp.sh
expdp system/"xxxx" directory=datapump tables=anbob.t1,ocs_anbob.return_step_detail_t filesize=1G dumpfile=ocs%U.dmp logfile=ocs.log parallel=4
#chmod +x dmp.sh
#nohup ./dmp.sh > longjobs.out 2>&1 &
[1] 7799188
#jobs
[1] + Running nohup ./dmp.sh > longjobs.out 2>&1 &
error output
# tail -f longjobs.out
Export: Release 11.2.0.3.0 - Production on Wed Dec 31 22:54:01 2014
Copyright (c) 1982, 2011, Oracle and/or its affiliates. All rights reserved.
Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Data Mining and Real Application Testing options
Starting "SYSTEM"."SYS_EXPORT_TABLE_01": system/******** directory=datapump tables=anbob.t1,ocs_anbob.return_step_detail_t filesize=1G dumpfile=ocs%U.dmp logfile=ocs.log parallel=4
Estimate in progress using BLOCKS method...
Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
Total estimation using BLOCKS method: 3.866 GB
Processing object type TABLE_EXPORT/TABLE/TABLE
Processing object type TABLE_EXPORT/TABLE/GRANT/OWNER_GRANT/OBJECT_GRANT
ORA-31693: Table data object "ANBOB"."T1":"PART_1" failed to load/unload and is being skipped due to error:
ORA-31617: unable to open dump file "/dsg/datapump/ocs02.dmp" for write
ORA-19505: failed to identify file "/dsg/datapump/ocs02.dmp"
ORA-27037: unable to obtain file status
IBM AIX RISC System/6000 Error: 2: No such file or directory
Additional information: 3
Processing object type TABLE_EXPORT/TABLE/COMMENT
Processing object type TABLE_EXPORT/TABLE/AUDIT_OBJ
ORA-31693: Table data object "ocs_anbob"."return_step_detail_t":"PART_1" failed to load/unload and is being skipped due to error:
ORA-31617: unable to open dump file "/dsg/datapump/ocs02.dmp" for write
ORA-19505: failed to identify file "/dsg/datapump/ocs02.dmp"
ORA-27037: unable to obtain file status
IBM AIX RISC System/6000 Error: 2: No such file or directory
database monitoring
select INST_ID,sid, serial#,program from gv$session s, dba_datapump_sessions d where s.saddr = d.saddr;
above will be show the expdp job cross 2 nodes.
Solution:
1. Create a directory object on clustered file system
2. Export without using parallel clause
expdp xx/xx dumpfile=test_%u.dmp logfile=test.log directory=temp_expdp schemas=test
3. Use CLUSTER option in expdp CLI
expdp xx/xx dumpfile=test_%u.dmp logfile=test.log directory=temp_expdp schemas=test cluster=n
This option will to constrain the job to run on the instance where it is started
references  oraclehandson note