Question HDD and SSD on caddy transfer speeds

[Luisito3107]

I have a ProBook 4540s with a 2 TB HDD, and recently I replaced the optical bay with a 12.7mm caddy to add a 1 TB SSD.
I checked with HWInfo and both SATA ports in my laptop aren't speed limited, and are detected as SATA 6.0 Gb/s.
The laptop can boot properly from the SSD at maximum transfer speed (560 MB/s), but when HDD is present as well, the SSD speed decreases to 190 to 300 MB/s.
I was thinking of switching the SSD to the main SATA port and the HDD to the caddy, but I read in some places that the maximum amount you can add in a caddy is 1 TB and my HDD is 2 TB.

It's recommended to switch the drives? What could happen to my HDD if I exceed that 1 TB limit? Should I try something else?

 

[falcon291]

I doubt that there is a limit to caddy drive, and I also doubt that HDD presence decreases the SSD speed.

Raw speed is different and higher than the actual speed. How did you test SSD speed?

 

[Luisito3107]

I doubt that there is a limit to caddy drive, and I also doubt that HDD presence decreases the SSD speed.

Raw speed is different and higher than the actual speed. How did you test SSD speed?

I tested the SSD speed under multiple conditions and in multiple devices. I used CrystalDiskMark, MiniTool Partition Wizard and Hard Disk Sentinel.
The first test I did was connecting the SSD through a SATA to USB adapter, but all the others I did by connecting the SSD in the caddy or on the main board.
I was thinking this could be a voltage problem. That perhaps, although the SATA port on the motherboard is not limited, it is not designed for those transfer speeds (when working in parallel with the HDD).