Ok, so dropping the cache is good.
How are you ensuring that you have one test setup on the HDDs and one on
the SSDs? i.e do you have 2 postgres instances? or are you using one
instance with tablespaces to locate the relevant tables? If the 2nd case
then you will get pollution of shared_buffers if you don't restart
between the HHD and SSD tests. If you have 2 instances then you need to
carefully check the parameters are set the same (and probably shut the
HDD instance down when testing the SSD etc).
I can see a couple of things in your setup that might pessimize the SDD
case:
- you have OS on the SSD - if you tests make the system swap then this
will wreck the SSD result
- you have RAID 0 SSD...some of the cheaper ones slow down when you do
this. maybe test with a single SSD
regards
Mark
On 18/07/18 01:04, Neto pr wrote (note snippage):
(echo 3> / proc / sys / vm / drop_caches;
discs:
- 2 units of Samsung Evo SSD 500 GB (mounted on ZERO RAID)
- 2 SATA 7500 Krpm HDD units - 1TB (mounted on ZERO RAID)
- The Operating System and the Postgresql DBMS are installed on the SSD disk.
