Optimizing Postgresql server and FreeBSD for heavy read and writes

Hello

I have a server dedicated for Postgres with the following specs:

RAM 16GB, 146GB SAS (15K) x 4 - RAID 10 with BBU, Dual Xeon E5345 @
2.33GHz
OS: FreeBSD 8.0

It runs multiple (approx 10) databases ranging from 500MB to over 24 GB in
size. All of them are of the same structure, and almost all of them have
very heavy read and writes.

pgtune (http://pgfoundry.org/projects/pgtune/) suggests the settings to be
changed as :

maintenance_work_mem = 960MB # pg_generate_conf wizard 2010-02-03
checkpoint_completion_target = 0.9 # pg_generate_conf wizard 2010-02-03
effective_cache_size = 11GB # pg_generate_conf wizard 2010-02-03
work_mem = 160MB # pg_generate_conf wizard 2010-02-03
wal_buffers = 8MB # pg_generate_conf wizard 2010-02-03
checkpoint_segments = 16 # pg_generate_conf wizard 2010-02-03
shared_buffers = 3840MB # pg_generate_conf wizard 2010-02-03
max_connections = 100 # pg_generate_conf wizard 2010-02-03

While this gives me the changes for postgresql.conf, I am not sure of of
the chnages that I need to make in FreeBSD to support such large memory
allocations. The last time I tried, Postgres refused to start and I had to
fall back to the default settings.

I would appreciate if somebody could point out the sysctl/loader.conf
settings that I need to have in FreeBSD.

With regards

Amitabh Kant