After we set the logon account same as the Oracle services, now the backup can go thru FT transport. But it only can run successfully for one job only. The subsequent job will still failed with error 6.
Once the RMAN backup job is failed, I straight trigger normal file backup via FT transport, it is still working fine.
Now the error in the dbclient is different:
17:46:51.532 [6336.10000] <4> handshake: INF - valid newdataSock: 5020
17:46:51.532 [6336.10000] <4> handshake: INF - nameSock = 3020, dataSock = 5020, commSock = 2516
17:46:51.532 [6336.9420] <16> CopyToShM: connection broken. Error #40
17:46:51.532 [6336.9420] <16> writeToServer: ERR - CopyToShM() failed, no files backed up
17:46:51.532 [6336.9420] <16> dbc_put: ERR - failed sending data to server
17:46:51.532 [6336.9420] <4> closeApi: entering closeApi.
17:46:51.532 [6336.9420] <4> closeApi: INF - EXIT STATUS 6: the backup failed to back up the requested files
17:46:51.532 [6336.9420] <4> closeApi: INF - closing commSock 4664
17:46:51.532 [6336.9420] <4> closeApi: INF - closing dataSock 4808
17:46:51.532 [6336.9420] <4> closeApi: INF - setting linger on nameSock 776
17:46:51.532 [6336.9420] <4> closeApi: INF - closing nameSock 776
17:46:51.532 [6336.9420] <16> VxBSASendData: ERR - Could not do a bsa_put().
17:46:51.532 [6336.9420] <2> xbsa_ProcessError: INF - entering
17:46:51.532 [6336.9420] <2> xbsa_ProcessError: INF - leaving
17:46:51.532 [6336.9420] <16> xbsa_SendData: ERR - VxBSASendData: Failed with error:
Server Status: Communication with the server has not been initiated or the server status has not been retrieved from the serve
17:46:51.532 [6336.9420] <2> sbterror: INF - entering
17:46:51.532 [6336.9420] <2> sbterror: INF - Error=7501: VxBSASendData: Failed with error:
Server Status: Communication with the server has not been initiated or the server status has not been retrieved from the serve.
It seems like there is some connection drop, but still can't manage to find where is it.