Asus Pro WS W680-ACE, SAS RAID adapter, PCIe bifurcation/reduced availability

[brisen]

Hello,

I have just made a new PC consisting of:

• Asus Pro WS W680-ACE IPMI motherboard
• i7 14700K CPU
• 64GB DDR5-6400 RAM
• NVMe Samsung 990 Pro in M.2_1
• 1 SSD in SATA6G_1
• 1 HDD in the SlimSAS header
• GFX is a Asus ProArt GeForce RTX™ 4070 SUPER 12GB GDDR6X OC Edition, PROART-RTX4070S-O12G, PCIe 4.0 x16, occupying 2.5 slot.

For now 2 PCIe slots are occupied, but I need/want to add more. Currently:

• PCIEX1(G3) - IPMI card
• PCIEX16(G5)_1 - GFX
• PCIEX16(G5)_2 - empty
• PCIEX16(G3)_1 - empty
• PCIEX16(G3)_2 - empty

One of the PCIEX16(G3) slots will host a PCIe 2.0 x1 card with 2 x internal USB3 19-pin headers (for a 5.25" card reader,), as the other USB ports on the MB are taken up by the IPMI card and the case USB headers.

I want to add a Broadcom MegaRAID 9560-8i or 9560-16i RAID adapter (PCIe 4.0 x8), and run 3+ HDD in RAID 5 (or 4+ HDD in RAID 6). I plan the HDDs to be WD Red Pro 16TB disks, speed of about 260 MB/sec.

But where should I put the RAID adapter? If it goes into one of the PCIEX16(G3) slots, the RAID adapter will be reduced to PCIe 3.0 x4, assumably also reducing bandwidth (but how many HDDs would it take to max out the bandwidth?). Or would it be better to move the GFX to the PCIEX16(G5)_2 slot, and putting the RAID adapter in the PCIEX16(G5)_1 slot; using PCIe x8/x8 bifurcation between the two slots - but how much will that affect the GFX's native PCIe 4.0 x16?

I need some help/advice on clarifying these things.

[Jiaszzz_ASUS]

Hello @brisen 

Thank you for reaching out to us.
Based on your setup requirement, we recommend referring to the instructions on page 1-8 of the Pro WS W680-ACE IPMI user manual:


You can try using a PCIe 4.0 x8 adapter card in the PCIEX16(G5)_2 slot to achieve x8 channel bandwidth, while the GPU installed in the PCIEX16(G5)_1 slot will indeed operate at x8 speeds.
The total bandwidth of PCIe 4.0 x16 is approximately 32 GB/s, while x8 offers half that, around 16 GB/s. This could lead to some bottlenecking in high-load scenarios, particularly at 4K resolution or higher, where significant data transfer is required (e.g., high-quality texture loading or in situations with limited video memory). However, at 1080p or 1440p resolutions, the impact on gaming performance is typically not noticeable.
Alternatively, if you choose to install the PCIe 4.0 x8 adapter card in one of the PCIEX16(G3) slots, it could indeed result in reduced speeds for the hard drive.
We suggest installing your devices based on your specific usage needs.

Thank you.