Why I Cannot detect the 3rd SATA HDD in the SYS-5028L-TN2, below is my HDDs install in chassis.
Total five HDDs:
mSATA SDD *1
SATA HDD *3 into the front bays slot
2.5" SSD *1 remove one SATA cable on M/B direct attach and install in chassis.
For 5028L-TN2 it supports MAX four SATA HDD or Three SATA HDD + One mSATA SSD, due to the mSATA port is shared with one of SATA3 ports, either the SATA3 ports are used or the mSATA port, but not at the same time.