Mac Pro 3,1, PCIe SSD operating at only 2.5GT/sec

[decryption]

I picked up a Mac Pro 3,1 pretty cheap and chucked in a Samsung SM951 PCIe SSD, sitting in a Lycom DT-120 M.2 PCIe SSD to PCIe 3.0 x4 adapter (both purchased from RamCity, heh). It works well and boots fine, but the transfer speed is limited to only around 700MB/sec.

Looking in system profiler shows me that whilst it's got 4x PCIe lanes, it's only operating at 2.5GT/sec, which would explain why benchmarking the SSD using Blackmagic's app only results in a max of 700MB/sec.



This leads me to believe it's in PCIe 1.0 mode for some reason. The Lycom DT-120 is supposed to be good at this, it supports PCI 3.0 and 2.0. Dunno why the Mac Pro 3,1 has decided to operate it in PCIe 1.0 mode. The SSD is in Slot 2 (next to the graphics card - which is operating happily in 16x 5GT/sec mode), which is supposed to have full 16x PCIe 2.0 speeds, regardless of what's plugged in to slot 1. Or am I wrong?

The only thing I can think of trying it another adapter off eBay (this one), but is there something else I'm missing here?

 

[h9826790]

This adaptor doesn't like x16 slot, try to put it on another slot and check the system info again.

 

[666sheep]

In other than x16 it will work @2.5GT/s for sure. PCIe 1,1 can't do more
OP: SM951 seems to don't like the 3,1 (another MR member had this exact issue with it). XP941 should work OK. It's tied to SM951 being PCIe 3.0 while XP941 is 2.0 and it negotiates the link properly with 3,1.

 

[h9826790]

My bad, I forget about that.

 

[decryption]

In other than x16 it will work @2.5GT/s for sure. PCIe 1,1 can't do more

That's right - I put it in the other slots just to see and there was no change.

OP: SM951 seems to don't like the 3,1 (another MR member had this exact issue with it). XP941 should work OK. It's tied to SM951 being PCIe 3.0 while XP941 is 2.0 and it negotiates the link properly with 3,1.

Damn, that sucks
Wonder if it'll work ok in a Mac Pro 4,1?

 

[Baunkjaer]

Damn, that sucks
Wonder if it'll work ok in a Mac Pro 4,1?[/QUOTE]
It works fine in the 5,1

 

[vicentk]

you can try to put the PCie in slot 2

 

[666sheep]

you can try to put the PCie in slot 2

If you'd click on his screenshot, you'd see the OP already has his SSD in Slot 2.
Your Plextor SSD is PCIe 2.0 x2 and does not have the same issue with 3,1 as PCIe 3.0 SM951 has.

 

[isisism]

.

 

[Theoprofil]

That's right - I put it in the other slots just to see and there was no change.



Damn, that sucks
Wonder if it'll work ok in a Mac Pro 4,1?

It works perfect on a mac pro 4.1 at slot number 3. Tested 100℅
[doublepost=1478913776][/doublepost]

In other than x16 it will work @2.5GT/s for sure. PCIe 1,1 can't do more
OP: SM951 seems to don't like the 3,1 (another MR member had this exact issue with it). XP941 should work OK. It's tied to SM951 being PCIe 3.0 while XP941 is 2.0 and it negotiates the link properly with 3,1.

XP 941 works perfect at 3.1 with 5.0Gt speed . Tested100℅ by me. Sm 951 works as 2.5gt again tested 100℅ by me.

 

[sevichenko]

thanks for the advice, i'm looking for a pcie ssd for my 3,1 MP

 

[Dan DC]

thanks for the advice, i'm looking for a pcie ssd for my 3,1 MP

Me too - what did you find?

 

[Cyberdoc71]

Sounds like those pcie slots are behind a plex chip i bet, if you used the primary gpu slot instead would not have an issue.

 

[freqrider]

3,1 does not perform bifurcation, like 4,1-5,1. (PCI switching.) You need to download and properly configure pcietools to turn on pcieII speeds on slot 2 or just install this>>>

GitHub - matatata/lnkspd: sets PCIe target link speed, uses pciutils lib and requires DirectHW.kext to run

sets PCIe target link speed, uses pciutils lib and requires DirectHW.kext to run - matatata/lnkspd

github.com