BigSur / OC : why is my Nvme GEN4 not at full speed ?


Recommended Posts

Hello !


I'll try to keep it short :

Fresh BigSur install (with Macinabox) on a 256Gb Samsung 980 PRO with the controller passed through.


The drive is on now on a PCIe Gen 4 socket but it may important to note that it was (my mistake) on a GEN3 socket during the install.


So before I moved it to the right socket, "System Report" reported : Link width : 4x / Link Speed 8GT/s (so GEN 3).


Now, it's on the right socket, the lspci command gives : LnkSta:  Speed 16GT/s (ok), Width x4 (ok)


BUT, and this is the problem I can't find a solution / explanation for : under System Report, Link Width is still 4x but there is no info for Link Speed... ???


A Blackmagicdesign Disk Speed test shows a read speed of 2.8GB/s (so the same as on GEN3) where the drive is theoretically capable of 7GB/s. And I know I wont get that speed, but now I'm having less than half.


Other details :

The same drive passed through (controller) to a windows VM is on a GEN4 link. So all good on this side.

Motherboard is Asus TUF Gaming X570. Latest bios.

The XML part for the controller :

    <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
        <address domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
      <alias name='hostdev0'/>
      <address type='pci' domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>




I even tried to move from Q35-4.2 to 5.1, but nothing changed.


My fear is that it's because I swapped socket after the install... And that the solution would be a new install... But maybe one of you will have a better suggestion !

Thanks for your attention.



Edited by bjornatic
Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.