I installed a new postgres 9.6 on both of my machines. I'm trying to measure the differences between the performances in each machine but it seems that the results arent accurate.
I did 2 tests :
Better phrased, I'd say the results aren't _stable_ -- 'inaccurate' suggests that pgbench is giving erroneous results; you've provided no evidence of that.
Storage performance can seem random; there are numerous complex processes and caching that are involved between the software layer and the storage. Some are within the database, some are within the underlying operating system, and some are within the storage itself. Spinning media is also notoriously capricious, various hard to control for factors (such as where the data precisely exists on the platter) can influence data seek and fetch times.
I think we can look ahead to a not too distant future where storage performance will be less important with regards to typical database performance than it is today. Clever people that are willing and able to buy appropriate hardware already live in this world essentially, but the enterprise storage industry seems strongly inclined to postpone this day of reckoning as long as possible for obviously selfish reasons.