[SOLVED] Slow Transfer Speed Between Two Internal SSDs

[fcp4life]

When transferring large files between two SSDs the transfer speed goes from high 400's MB/s down to 17-20MB/s. I understand there is a cache but I feel like those are USB speeds, not internal SSDs ones. I have enabled write cache, and even set my pc to high performance power mode. Both SSDs are connected internally via SATA III 6G.
I am transferring the data between

• Samsung 860 EVO 1tb ( MZ-76E1T0B/AM)
• Silicon Power 1TB SSD 3D NAND A55 (SP001TBSS3A55S25)

If it matters... my PC specs are...

• Motherboard - ASUS Z170-A
• CPU - I7 - 6700K
• Memory - G.SKILL Ripjaws V Series 64GB DDR4 3200 (PC4 25600)

 

[rgd1101]

how full is the ssd?

 

[USAFRet]

How much data, and how many files?
A single file of 200GB will be MUCH faster than 20,000 small files totaling 200GB.