question about ASUS Pro WS B850M-ACE SE

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fdie:)nohomelab

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Jun 1, 2026
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Hi Guys,

I'm looking to buy this motherboard for my first nas server build and I was wondering what everyone's experience with this motherboard is. I am thinking about making this an all flash nas with the top pcie slot occupied by the m.2 adapter card. Does anyone know if there is pcie bifurcation with this motherboard? I have asked Asus and that will take a while for them to reply to me and there's not much documentation on Asus's pcie bifurcation table thread or youtube.

Thank you in advance !
 
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etorix

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Sep 28, 2021
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Generally, AMD CPUs (including EPYC 4000) should bifurcate x4x4x4x4, while APUs only do x8x4x4. We can only hope that Asus implemented that properly on a "Pro WS" board.

But your pick looks like massive overkill for a NAS with respect to CPU power and massive underkill with respect to PCIe lanes if you want a NVMe-based NAS. If you only need 4 NVMe, Broadwell-era Xeon D-1500 CPUs can do that, and are powerful enough for NAS duties at 10 Gb/s, so you might look into some Supermicro X10SDV board (v.2).
If you may need more than 4 NVMe, look into old Xeon Scalable (or old EYC 7000) for more PCIe lanes.
 
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fdie:)nohomelab

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Jun 1, 2026
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etorix said:
Generally, AMD CPUs (including EPYC 4000) should bifurcate x4x4x4x4, while APUs only do x8x4x4. We can only hope that Asus implemented that properly on a "Pro WS" board.

But your pick looks like massive overkill for a NAS with respect to CPU power and massive underkill with respect to PCIe lanes if you want a NVMe-based NAS. If you only need 4 NVMe, Broadwell-era Xeon D-1500 CPUs can do that, and are powerful enough for NAS duties at 10 Gb/s, so you might look into some Supermicro X10SDV board (v.2).
If you may need more than 4 NVMe, look into old Xeon Scalable (or old EYC 7000) for more PCIe lanes.
Click to expand...
Thanks for the reply!

I agree that in terms of cpu power its probably overkill running truenas by itself, I don't think I can run proxmox as I don't have enough ram for some other services but more than enough for truenas. I plan to have a little more than 4 drives ~ 6 if possible. these are gen 4 drives which I really want to make use of and will probably have a sfp+ or higher nic later on when my network can handle it.

I have had a look at epyc 7002 ~ 7532 chips and they really do have all I can ask for but my main thing is that with the am5 platform I can kind of split hdds nas for cold storage and archival, and my all flash based nas into different nodes that are generally more power efficient. I would be able to power on and off my hdd nas on a need be basis; say for example maybe need it to be turned on for backups and archival from the all flash based nas. And from my estimation its probably going to be less power draw if I go ahead with am5 or this motherboard and upgrade to epyc 4545p when I have more budget and need. Also do note that I live in a tropical environment so it gets pretty hot year round and I would rather for something that isn't going to melt my face off when I go to service it. :)

The only downside I see to this approach is the overall increase in cost from building 2 or more extra nodes.

In the future I may decide to go down the Epyc 7000 route when I need to have more vm's but I'm currently unsure if I will ever need more and what that will be used for.
 
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etorix

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Sep 28, 2021
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fdie:)nohomelab said:
these are gen 4 drives which I really want to make use of and will probably have a sfp+ or higher nic later on when my network can handle it.
Click to expand...
Gen 4 does not matter, as the NAS will be bottlenecked by the NIC anyway ;)
And if the switch is not too far from the NAS, you may as well use the on-board 10GBase-T, with a RJ45 transceiver if need be. Or get a cheaper motherboard. There's no point wasting money and PCIe lanes on a 10G NIC you won't use.
 
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fdie:)nohomelab

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etorix said:
Gen 4 does not matter, as the NAS will be bottlenecked by the NIC anyway ;)
And if the switch is not too far from the NAS, you may as well use the on-board 10GBase-T, with a RJ45 transceiver if need be. Or get a cheaper motherboard. There's no point wasting money and PCIe lanes on a 10G NIC you won't use.
Click to expand...
yes makes a lot sense, I will try to upgrade to 40gbe when I have the money to upgrade the rest of the network. But until then it will be a really cool and power efficient nas :) and I don't have to worry about my nic being set on fire.
 
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