Noob questions regarding RAC database

Question

Hi,
I've run a number of Oracle servers, but I'm just now labbing my first RAC server. Firstly, I'm having some inconsistencies with regards to logging in. Observe:
[oracle@rac1 ~]$ echo $ORACLE_SID
daradb
[oracle@rac1 ~]$ sqlplus system
SQL*Plus: Release 11.1.0.6.0 - Production on Tue Jul 7 06:10:09 2009
Copyright (c) 1982, 2007, Oracle. All rights reserved.
Enter password:
ERROR:
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
Linux Error: 2: No such file or directory
[oracle@rac1 ~]$ sqlplus system@daradb
SQL*Plus: Release 11.1.0.6.0 - Production on Tue Jul 7 06:10:24 2009
Copyright (c) 1982, 2007, Oracle. All rights reserved.
Enter password:
Connected to:
Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - Production
With the Partitioning, Real Application Clusters, OLAP, Data Mining
and Real Application Testing options
SQL>
In any previous experience, setting ORACLE_SID to daradb would mean that @daradb was unnecessary. What am I missing in this regard?
The second issue being, I don't ever seem to be able to logon using the standard OS authentication I'm used to:
[oracle@rac1 ~]$ sqlplus /@daradb
SQL*Plus: Release 11.1.0.6.0 - Production on Tue Jul 7 06:16:56 2009
Copyright (c) 1982, 2007, Oracle. All rights reserved.
ERROR:
ORA-01017: invalid username/password; logon denied
[oracle@rac1 ~]$ sqlplus /@daradb as sysdba
SQL*Plus: Release 11.1.0.6.0 - Production on Tue Jul 7 06:18:23 2009
Copyright (c) 1982, 2007, Oracle. All rights reserved.
ERROR:
ORA-01031: insufficient privileges
It's not really an issue in the sense that I can still get in using system/password, but it's important I grasp what's going on before I proceed.
Background: Initially I couldn't logon at all. For some reason it appears that tnsnames.ora was installed by the dbca wizard under the ASM_HOME, instead of ORACLE_HOME. I copied it to the correct place to enable connection.

Answer 1

Thanks sybrand. You are correct about the naming assumption. Accordingly the following allows me to more specifically logon to the chosen server:
[oracle@rac1 daradb]$ sqlplus system@daradb1
or
[oracle@rac1 daradb]$ sqlplus system@daradb2
However using either of these SIDs doesn't appear to change this issue.
[oracle@rac1 daradb]$ ORACLE_SID=daradb1 sqlplus system
SQL*Plus: Release 11.1.0.6.0 - Production on Tue Jul 7 07:31:40 2009
Copyright (c) 1982, 2007, Oracle. All rights reserved.
Enter password:
ERROR:
ORA-01034: ORACLE not available
It still requires the @daradb1.
Regarding permissions, I'm somewhat lost.
[oracle@rac1 daradb]$ id
uid=500(oracle) gid=502(oinstall) groups=501(dba),502(oinstall)