I get your issue. I work on 3010's on the regular at work and have taken a few home when they were decommissioned. I use them for all sorts of things and have had this same issue. This is a Dell imposed limitation between their different models of 3010's. If you look at the technical guidebook there is a section showing the different SATA ports for each and only on the full size does it have 4 active ports, the DT model only has 2 activated, even though it has 4 physical ports on the board.
There is a work around for this. It is a little long winded and seems strange, but I can confirm my 3010 DT is able to use all 4 SATA ports.
Here we go:
1.) Shutdown your PC
2.) Open your case and find the green USB 2.0 Headers
3.) Plug your green header onto the blue header
4.) Turn on your PC and you will get an error saying that the front I/O has an error
5.) Enter your BIOS and you should now see 4 SATA ports, they are not functioning yet though, even if they see a drive.
6.) Shutdown again and swap your USB header back to the green headers
7.) Start up again and you will get another Front I/O error that you can ignore
8.) Enter your BIOS and you should still see all 4 SATA ports active
9.) Change your boot option from Legacy to UEFI and save the BIOS
10.) Restart and let it try to boot normally, mine tried to go to PXE boot
11.) Once the PXE boot either fails or you power off the computer go back into your BIOS and change the boot option back to Legacy
12.) Save your BIOS.
13.) Boot into Windows and you should be able to use/access your drives.
Just a heads up, if you make any changes to those extra drives, even just swapping to the other SATA port, you have to repeat steps 9 -13 to access them again.
Another note: Your front I/O will function just fine the whole time even though its says there's errors.
I figured this all out this morning as I am using a 3010 board/cpu to set up a PLEX server and I need those 2 extra ports as well. I didn't want to spend the extra money on a PCIe card for more SATA.
As a side note if you ever move a 3010 to another case, you need to bring along the power switch. Its proprietary on this board.