Q: Link Speed vs. Negotiated Speed
Hello:
I recently added an external SSD to my iMac (Model 14,1) which is a late 2913 21.5 Inch system. I was very happy with the resulting performance boost. I did some testing with BlackMagic Disk Speed Test which yielded some interesting results. My external SSD on USB 3.0 ran about 380 MB/s write and 430 MB/s read. I also have an external Toshiba drive (3 TB 5700 rotational speed) on the USB 3.0 which yielded 130 MB/s write and 125 MB/s read. Finally I tested my internal HDD (1 TB 5400 rotational speed) which peaked at 70 MB/s read and write. I was surprised by these results as I expected the internal HDD to be faster than the external 3 TB HDD.
Looking at the system report I see that my SATA bus is an Intel series 8 chipset that is capable of 6 Gbps transfer rate but the negotiated link is 3 Gbps, which would certainly explain why my internal drive has the slowest transfer rates. My question is is this normal? Is the hardware behaving to spec or do I need to make an adjustment and or bring it in for service? I am pretty tech savvy so I can make adjustments if needed; just need to know how.
Thanks.
iMac, OS X El Capitan (10.11.6), 21.5 inch late 2013 8 GB RAM 1 TB H
Posted on Aug 17, 2016 7:43 PM

