No post for external GPU using slimsas

[sappireflames00]

Hello, I have a dl385 gen 10 plus server., It is functional for the most part. However I am trying to install an external gpu (because the gpu is physically too big for the server) using a PCIE x16 to slimsas. tot then a slimsas riser. I've tested another GPU in the PCIE slot as normal and in this case the server recognizes the card normally. However once I try to use slimsas, nothing ever shows. The server doesn't pick up the riser or anything., I have tried multiple risers, cables, nothing. A while back I tried the same setup on a consumer board, a b550 I think, and it worked. So I'm a little confused, does anyone know if there is a bios setting or something? Maybe an OS setting? I am using proxmox 8.4.0, but like I said, the other card I tried was registered just fine.  Any help would be greatly appreciated. Thanks. 

[MTRenato]

Hi,

It seems like the slim SAS riser you're using isn't ideal for connecting GPUs, as it's designed for SAS devices. I recommend trying a high-quality PCIe x16 riser specifically for GPUs. Also check the BIOS to ensure the PCIe slots are configured correctly (bandwidth and operation mode).
If you're using Proxmox in a virtualized environment make sure PCIe pass-through is properly configured.

Hope that helps.

[Mamatha_J]

Hi @sappireflames00 

1. Look in the UEFI settings for PCIe configuration.

2. Ensure system BIOS / UEFI / platform ROM / BMC / iLO firmware are fully up to date (as per HPE’s supported versions). Some firmware fixes might add or remove limitations on external paths.

3. External cables and risers can degrade signal quality. Check for adequate shielding, minimal length, proper impedance, and clean connectors. Also, the GPU / riser might need external power or auxiliary rails that aren’t being provided.

4. Ensure that all sideband lines (CLK, REFCLK, PERST#, presence detect pins) are properly connected through your SlimSAS + riser chain. If the server cannot see presence detect or reset, it may not enumerate the device.

5. Try a shorter, simpler PCIe extension (e.g. PCIe extender ribbon, or a short active extender) instead of SlimSAS, to test whether the server enumerates anything externally.

6. Boot the server into UEFI / System Diagnostics and look for PCIe device enumeration messages. Also check system event / iLO logs to see whether the link attempts to train or fails.

7. On your B550 consumer board, your SlimSAS + riser chain worked, but that board likely has more flexible / permissive PCIe routing logic. The HPE server board may “hide” or filter unrecognized paths.

8. If your setup is outside what HPE’s official documentation supports (external GPU chain, etc.), accept that it might not be possible under firmware constraints. In that case, internal smaller GPU options (if possible) or switching to a server model that supports external accelerators (e.g. GPU expansion chassis) might be required.

Thanks & Regards,

Mamatha Ajaraddi

[Mamatha_J]

Hi @sappireflames00 

Please let us know if you were able to resolve the issue.

If you are satisfied with the answer, then kindly click the "Accept As Solution" button for the most helpful response so that it is beneficial to all community members.

Thanks & Regards,

Mamatha Ajaraddi