we've had the same experience here - with older SATA 2 (3Gbps) - in spite of SSD having no spin latency, the bus speed itself was half of the SAS-2 (6Gbps) we were using at the time which negated SSD perf in this area. HDD was about the same perf as SSD for us.
Someone help me analyze the two execution plans below (Explain ANALYZE used), is the query 9 of TPC-H benchmark [1]. I'm using a server HP Intel Xeon 2.8GHz/4-core - Memory 8GB HDD SAS 320GB 15 Krpm AND SSD Sansung EVO 500GB. My DBMS parameters presents in postgresql.conf is default, but in SSD I have changed random_page_cost = 1.0.
you are comparing a SAS Drive against a SATA SSD. Their interfaces serve a completely different bandwidth. While a SAS-3 device does 12 Gbit/s SATA-3 device is only able to transfer 6 Gbit/s (a current SAS-4 reaches 22.5 Gbit/s) Do a short research on SAS vs SATA and then use a SAS SSD for comparison :)