Problem while pg_xlog directory

Dear all,

I am doing some Performance tuning in Pgsql. I have changed several
Parameters in postgresql.conf file. Now I want to change my pg_xlog
directory to another disk.

I followed the below steps :

cd /hrd2-p/postgres_data
> /etc/init.d/postgresql-8.4 stop
> mkdir -p /opt/pg_xlog
> chown -R  postgres.postgres /opt/pg_xlog
> chmod 700 /opt/pg_xlog
> cp -rf pg_xlog/* /opt/pg_xlog
> mv pg_xlog pg_xlog_old
> ln -s /opt/pg_xlog pg_xlog
> /etc/init.d/postgresql-8.4 start

But me server fail to start and there is empty log in startup.log. I also checked my permissions and directories are
ownedby postgres user. 

Is I am failing something and there is some simple way.

Also, i want to know after Performance tuning following the below link :

http://wiki.postgresql.org/wiki/Performance_Optimization.

How much our performance increases.

I am selecting data from 5Gb file and it takes 229477 ms.
Still i execute same query in 226977 ms after some tuning.

Please help.


Best Regards

Adarsh Sharma