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I had a case in the past with a customer where even after increasing the disk size, it didn't help much after some time.
What I did was check the 'postgres debugging' logs that were enabled and had to turn it off in order to fixed.
Run on the SMS:
[Expert@MGMT:0]# cat  /opt/CPshrd-R81.20/database/postgresql/data/postgresql.conf | grep logging_collector

                                        # requires logging_collector to be on.

logging_collector = on          # Enable capturing of stderr and csvlog

I had to set the logging_collector to off in order to fix it. 
But don't just change the parameter with vi, there is a script to do it.
Advise to ask TAC for it and run with them.
In that time the script was under '/opt/CPsuite-R81.20/fw1/scripts/postgres_logs_off.sh'
Regards