Discussion at http://postgresql.1045698.n5.nabble.com/parallel-pg-dump-td5615118.html
Used patch in parallel branch of https://github.com/adunstan/postgresql-dev.git
hardware: Dell PowerEdge R510
os Ubuntu 12.04.1 LTS
cpu: 8 Intel(R) Xeon(R) CPU E5607 @ 2.27GHz
memory: 32 GB
pg_version: psql (PostgreSQL) 9.1.6
postgres=# SELECT pg_size_pretty(pg_database_size('portals'));
pg_size_pretty
----------------
1604 GB
Size on disk: 121G
time pg_dump -p 5433 --format=directory --compress=9 --lock-wait-timeout=2000 --create --oids portals -f /volumes/parkinglot/pgbackups/pg_dump_dir_test
real 1090m14.893s
user 943m16.329s
sys 13m33.555s
time /tmp/pg_dump_parallel -p 5433 --jobs=2 --format=directory --compress=9 --lock-wait-timeout=2000 --create --oids portals -f /volumes/parkinglot/pgbackups/para_pg_dump_test2 --no-synchronized-snapshots
real 469m5.578s
user 821m52.678s
sys 11m33.503s
time /tmp/pg_dump_parallel -p 5433 --jobs=3 --format=directory --compress=9 --lock-wait-timeout=2000 --create --oids portals -f /volumes/parkinglot/pgbackups/para_pg_dump_test3 --no-synchronized-snapshots
real 331m0.277s
user 852m26.268s
sys 12m22.502s
time /tmp/pg_dump_parallel -p 5433 --jobs=4 --format=directory --compress=9 --lock-wait-timeout=2000 --create --oids portals -f /volumes/parkinglot/science/para_pg_dump_test4 --no-synchronized-snapshots
real 215m50.723s
user 729m57.141s
sys 8m17.663s