How to tell if data checksum feature is on in Postgres

You can use pg_controldata see if your postgresql cluster enable data_checksum. if version=0 then your cluster disable the function. And data_checksums parameter add by PostgreSQL 9.3.4, if your postgresql version small than that, you cannt select this guc parameter. you must check it by control file.

pg93@db-172-16-3-150-> pg_controldata |grep checksum
Data page checksum version:           0

show data_checksums;
 data_checksums 
----------------
 off

http://www.postgresql.org/docs/current/static/runtime-config-preset.html