Seeking performance advice and explanation for high I/O on 8.3

Would love to get some advice on how to change my conf settings / setup
to get better I/O performance.

Server Specs:

2x Intel Xeon Quad Core (@2 Ghz - Clovertown,L5335)

4GB RAM

4x Seagate 73GB SAS HDD 10k RPM - in RAID ( stripped and mirrored )

FreeBSD 6.4

Apache 2.2

PostgreSQL 8.3.6

PHP 5.2.9

~1500 databases w/ ~60 tables each

Total I/O (these number are pretty constant throughout the day):

Reads: ~ 100 / sec for about 2.6 Mb/sec

Writes: ~ 400 /sec for about 46.1Mb/sec

Conf settings:

listen_addresses = '*'

max_connections = 600

ssl = on

password_encryption = on

shared_buffers = 1GB

work_mem = 5MB

maintenance_work_mem = 256MB

max_fsm_pages = 2800000

max_fsm_relations = 160000

synchronous_commit = off

checkpoint_segments = 6

checkpoint_warning = 30s

effective_cache_size = 1GB

pg_stat_bgwriter:

checkpoints_timed: 16660

checkpoints_req: 1309

buffers_checkpoint: 656346

buffers_clean: 120922

maxwritten_clean: 1

buffers_backend: 167623

buffers_alloc: 472802349

This server also handles web traffic and PHP script processing.

Most of the SQL happening is selects - very little inserts, updates and
deletes comparatively.

I have noticed that most/all of the I/O activity is coming from the
stats collector and autovacuum processes. Would turning off the stats
collector and autovacuum be helpeful / recommended? Could I change my
checkpoint_* or bgwriter_* conf values to help?

Let me know if you need more information / stats.

Any help would be much appreciated.

Thanks,

Scott Otis

CIO / Lead Developer

Intand

www.intand.com