Question MSI Pro B550M-VC PCIE lane sharing

[ctlane]

I'm about ready to pull the trigger on purchasing it, but I can't find any info on the PCIE lane sharing. I know that M.2_1 is Gen4x4 to the CPU and M.2_2 is Gen3x4 to the chipset. However, there's no info in the manual or anywhere else I could find on what happens if you populate both. I don't mind giving up a SATA slot, but I sure don't want to see the GPU suddenly drop from x16 to x8. Also, I couldn't find out whether both slots are bootable or just M.2_1. Thanks!

 

[Lutfij]

Welcome to the forums, newcomer!

You're going to be fine with lane allocations. Both the M.2 slots will operate at max speeds and yes you can have the OS drive on either of the slots.

 

[ctlane]

Thanks so much, but where in the world could I have found this info without a guru like you available? I read the spec sheet & manual and googled my fingers to the bone, but no dice. Pretty stoked for this 1440p build though!-)

 

[ctlane]

I've been meaning for months to update this thread. I was able to put my gaming drive in the faster m.2_1 slot and the boot drive in the slower m2._2 slot. However, something in the MSI firmware spends about 30 seconds trying to recognize m.1_1 as a boot drive before finally checking m.2_2. It's a bummer to have the system booting in 40s rather than 10s, but it's blazing fast once booted.

 

[ctlane]

After suffering with this for months, I had occasion to crack my case for maintenance & decided to swap the M.2 drives. First boot took 15s - glorious! Did a little work/play & after a Windows reboot was back to 40s. WTF? Noticed odd power cycling to my USB keyboard during POST & combined that with my PDP wired Xbox controller never being recognized by Windows (Error 43 in Device Manager) on boot (though it worked fine after replugging). After unplugging all USB devices & selectively replugging them on several boots, I discovered that the PDP is responding to the poll of USB ports in a manner that locks up POST for >20s. Unplugging that controller at shutdown each day gives me a fast boot every time. Weird! (Coda: Cheap generic Xbox controller does not provoke this behavior so definitely an issue with PDP rather than MSI USB.)