Link Speed and Negotiated Link Speed in my Mac Mini (Mid 2010)

But isn't the issue you're having related to your 320GB HDD, not an SSD? Or did I miss something in this thread? 🙂

I had the same problem with the 750GB SSD that I installed in my wife's computer, and was extremely frustrated trying to find a solution. Bottom line is there isn't a good solution, but there is one that seems to work pretty consistently for me. I still, on restarts have the interface come up at 1.5GB but am able, through successive restarts to get the link back to 3GB. See pics below:

So the original suggestion was to reset the SMC from a cold power off, and that is how I got it the first time. However, after successive restarts it would sometimes revert down to 1.5 again. It seems restarting and resetting the PRAM sometimes helps but I have got it to negotiate at 3GB just by restarting the computer. In any case, that is the solution that works consistently for me on this computer and on my Mac Pro. Let me know if you can get it to work out for you as well. Good luck.

Success NVIDIA MCP79 Mac Mini mid 2010, Samsung 840 EVO SSD, 3 Gb / negotiated 3 Gb, SATA II

Reply • Like Show 0 Likes(0)

This post is getting a bit dated, but I wanted to share my own (similar) boggling experience with the Link Speed & Negotiated Link Speed situation on 'older' Mac h/w, specifically h/w using a NVidia MCP79 ACHI.

Specifics: 2.93 Ghz iMac early 2009 24". Link speed: 3.0 Gigabit. Currently running Yosemite 10.10.2

What I did: Replaced the 'failed' original (2009) 640 GB WD 6400AAKS SATA 2 (3.0 Gb/s) HDD 16 MB Cache (~ a WD Caviar Blue w/ Apple label ~) with a 2014 1 TB WD10EZEX Caviar Blue SATA 3 (6.0 Gb/s) HDD 64 MB Cache drive. No issues whatsoever with the teardown/replace/restart/etc. The entire process should take not more than ~ 1 hour, being careful not to rush or force things. The 'shear volume' of dust removed from the heat-vents, circuit board & fans was monumental! After this 'upgrade' the average operating temperate dropped 'significantly', as did the number of NVDA kernel panics that had been happening for years+ (i.e none).

Observations: I do know that under Snow Leopard (10.6.8) the original HDD would always negotiate a HDD link speed at 3.0 Gigabit. After replacing the failed original drive, w/ the noted 1 TB Caviar Blue (noted above), the HDD would either have a negotiated link speed of 3.0 Gigabit OR 1.5 Gigabit. During the times when the 'new' HDD would connect to the NVidia board @ 3.0 Gigabit, Blackmagic Disk Speed Test would show sustained read & write speeds of ~ 155 MB/s. During the times when the 'new' HDD would connect to the NVidia board @ 1.5 Gigabit, Blackmagic Disk Speed Test would show sustained read & write speeds of ~ 110 MB/s. I tried a number of options to try to reliably replicate when the new HDD would have a negotiated link speed of 3.0 Gigabit (resetting PRAM, resetting SMC, etc) - HOWEVER, there was no specific, repeatable pattern as to when/why the new HDD would show a negotiated link speed of 3.0 Gigabit or 1.5 Gigabit.

Sol'n: I'm still not 100% sure if the 'random' negotiated link speed issue is related to Yosemite (on an early 2009 iMac), or the NVidia MCP79 ACHI, or both. Here's what I did. I disassembled my iMac (again) to allow access to the jumper pins on the WD Caviar Blue 1 TB SATA 3 drive & used a jumper (from an older G4 PowerMac in my tech 'waste-bin) on pins 5 & 6 (as Western Digital suggests to overside SATA 3 (6.0 Gigabit) HDD's to connect at SATA 2 (3.0 Gigabit) speeds). I realize that 'jumpers should not be required' in this day & age with auto-negotiating logicboards/etc - but in my situation my 'new' WD 1TB drive (jumpered on pins 5 & 6) will now 'always' show a negotiated link speed of 3.0 Gigabit + the Blackmagic Disk Speed Tests consistently show 150-160 MB/s read & write speeds.

Takeaway: It's possible that Yosemite now only knows about SATA 3 (& faster) HDD's &/or SSD's, whereby if the system does not see an actual SATA 3 :: SATA 3 HDD/Logic-board connection, it forces a drop to SATA 1. The other (more likely) possibility is that the NVidia MCP79 ACHI board (in the iMac early 2009 & other Mac systems) is not 'intelligent/robust' enough to assign a proper negotiated link speed to SATA 3 HDD's on a consistent basis. Possibly yet another (+growing+) example of defective/buggy/weak NVidia h/w embedded into Mac products.

While this is not 100% the issue of the OP (though, perhaps close), it may shed some light/help others with older Mac h/w who end up with sub-optimized HDD real-world DIY 'upgrades'. I can't speak for negotiated link speeds for SATA 3 or SATA 2 SSD's on this particular system.

-Jeff

This answer gave me hope but I realized my hard disk doesn't have jumpers.

Here is my situation: Mac Mini (late 2009) with Yosemite. I still have the original HD installed, I upgraded the RAM to 8 GB.

I don't know if, in the past, my negotiated link speed was 3 Gb, but since when I discovered this issue I could never brought it over 1.5 (PRAM and SMC reset useless). I think it should be 3! Blackmagic shows a write/read speed of ~ 37 MB/s (how bad is that?)

My HD has more than 5 years now, close to its end of life. I am very dubious on what to buy next. My first idea was a Western Digital WD7500BPKX Black (does it have jumpers that allow to force SATA II?), but the fear of having this stuck at 1.5 is pulling me back. The other idea is a Crucial SSD MX100 (almost any other SSD has problems with that Nvidia connector) since it seems that people with this Mini model and that SSD achieve 3 Gb speed.

37MB/s is about right for an older mechanical drive, 50 to 75 for a modern 7200 high density drive (500GB+ per platter). The Crucial SSD should give you 250MB/s on a Sata 2 bus.

I have a Mac Mini 2009 with the NVidia SATA controller. I tried the Samsung EVO 250GB SSD and it was not able to do more than 1.5Gb. From this post you will see that there is a problem with some drives not talking well with the NVidia SATA controller. There were reports of the Crucial SSD drives working well so I returned the Samsung EVO and ordered a Crucial BX100 250GB since I could not find a Crucial M500.

It said on the Crucial website that this drive is compatible for the 2009 Mac Mini. Of course all 6Gb drives "work" but the negotiating speed is the culprit.

When I installed the BX100 250GB I was disappointed because it also was set to 1.5Gb! I was on a chat with Crucial on their website and they suggested there must be something with "garbage collection" and to fix it I should take out the drive and let it stay connected to power only (no data connection) for at least 8 hours and the drive would fix itself. This sounded like a crazy solution but ok, I will try it. To my my amazement this really worked! Look at the enclosed pics. I get at least twice the speed I had on 1.5Gb. So my conclusion is that Crucial SSD drives work with the NVidia SATA controller in the 2009 Mac Mini. I guess this should work also with other Crucial SSDs.

So guess what. I have some more interesting content to my experience!

- I upgraded to OS X 10.10 and the the drive was back to 1.5GB/s 😠

- Installed Trim Enabler and it was back to 3GB/s. Horay again!

- I upgraded OS X 10.10 to 10.10.5 and the drive was back to 1.5GB/s 😮

So I took the drive out and let it run on only power again for 8 hours.

It has since been stable on 3GB/s. What a frustrating job with a happy ending. Hopefully still happy. Like you wrote @Vajpai this might work with other drives but I doubt the Samsung drives. But then I have not tried after disassembling the Mac Mini so many times. If it works, don't touch it right?

Yes @Vajpai, I am afraid that the major update to OS X 10.11 would break things again would set back the drive to 1.5Gb/s so I think I will keep the system like it is. I wonder really if this is a hardware or a software problem, or both. Will post if I dare to do the upgrade!