Can I connect a SATA disk on a SAS connector on the motherboard?

Can I connect SATA drives to SAS connectors?

Yes, well known question / answer

Does the 6 Gb/s transfer rate means that I'll get an equivalent of SATA 3 (which is important if I use SATA 3 SSDs)?

Yes. They will negotiate the speed, slower device wins (12G sas ctrl will lower speed to sata 2 drive if needed) or drive will lower speed to older SAS controller. MSM software (or BIOS) can show you negotiated speeds.

Are there drawbacks using SAS connectors instead of SATA 3 ones for SATA 2 and SATA 3 drives? In other words, if the motherboard has both SATA 3 and SAS connectors, what is the reason, if any, to use SATA 3 connectors for SATA drives?

Use SAS. Usually SATA connector are part of Intel southbridge. Tests I've done show throughput drops proportionally to number of SATA drives connected to southbridge and results were horrific for 6 drives used simultaneously on Intel southbridge.

SAS controller on your motherboard is probably LSI using 4 pcie lanes - throughput was the same if you use 1 or 12 SAS drives (i lost the link to that blog I made).

Yes you might have to buy appropriate SAS cable (it's another topic, cheap on ebay from china).

The only reason where you might not use SAS is when BIOS doesn't allow booting from SAS drive (but todays everyone boots from NVME anyway).

Here is a test of my SAS setup, 16 drives on expander (expander slows things down, but results are shockingly better than you would achieve with intel southbridge).

Simultaneous test of 6GB eMLC on 12GB controller + 24 port SAS expander. Doesn't matter if drive is sas or sata.

You can usually (but not always) connect SATA drives to a SAS backplane - where the motherboard is designed to support it it will work, however there are a surprising number of corner cases - For example I help maintain a Dell Mass Storage array - it has an SAS backplane. You can plug a SATA drive in it and it will work - sort-of - until it causes corruption. You can get an "Interposer" to make a SATA drive work with an SAS backplane from Dell - of-course its not free.

On the otherhand, I've used SATA drives directly in Intel and HP systems without issues (well, without issues accepting SATA drives, the HP systems were older and did not like drives > 2TB).

Normally the spec sheet will tell you what drives are supported, although its usually not comprehensive.

The Wikipedia says

SAS offers backward compatibility with SATA, versions 2 and later. This allows for SATA drives to be connected to SAS backplanes. The reverse, connecting SAS drives to SATA backplanes, is not possible.

So...

• yes
• yes
• the reason to use a SATA port for a SATA drive? The things are kind of meant to go that way... If you want to connect the SATA drive to the SAS port, you'll need a breakout cable. The SAS port on your motherboard is probably the SFF-8087, but please double check that. If it is the case, you'll need something like this

Good luck :)