I’m currently setting up my first VFIO build. Is there anything to look out for when choosing a second GPU? The one passed through will be an RX580. For the host I’m looking for something cheap, good linux compatibility (so something AMD i guess?), low power usage and ideally it can use one of the PCI 2 x1 slots. I need the other x16 slots for other cards. I think I can saw off some parts of a 16x PCI card but I’d like to avoid that if possible. The host GPU does not really need to do anything fancy.
Zotac used to make 1x pci-e graphics cards. I think there is a gt 710 (!) and maybe a few older AMD options.
Does the x1 slot have an open end, or is the end solid plastic?
Some x1/x4/x8 slots have the end open so they’ll fit larger cards.
Anyways, there’s the GT1030 if you want something newer, but the GT710 is a popular basic GPU as well.
I purchased a 4GB polaris card (like rx450 or rx460/560) with 6 pin pcie power connector and I cut the “lower” pcie-1x slot (farthest from cpu) with a dremel so I can plug any card into it. On a board like the x370 taichi I could plug a usb card into the top slot, vega into second slot, x460 into that 1x slot, nvme into bottom nvme slot, and still have the 8x slot free for use by something else. The power connector insures better compatibility, but would be a pain in some configs. Note that there is a radeon pro version of polaris rx460 that is single slot. Otherwise you have to replace the cooler on any other polaris card with one from an older gpu from ebay. The 4GB assures that you can run web browsers, video playback software, and some 3d printer design tools and repetier host without running out of vram. On a 2 GB card you might run out of VRAM depending on what you might be doing on the host. Polaris cards work great. Note that when the VM isn’t running you better learn how to use PRIME switching with VM scripts to your use gpu for gaming afterwords. Older AMD cards do work with the amdgpu driver once you enable support with the kernel boot options. However in some cases resume from standby might be broken, but I also see that there may be a kernel patch. It would be better to spend a few extra dollars for polaris though as driver support is much better. The pro cards are now cheaper than before if you shop around, so you might able to snag the quad display port 4gb single slot models for under $200.
There are ancient 1x quadros for save for like $10 on ebay, but not sure those are great.
GT710 is your best bet IMO, but AMD have some low power cards too from that era.
Typically 1x cards are overpriced but look around. No reason to do the dremel thing anymore IMO. Install the low profile bracket, buy a cheap mining riser and install it in the regular slot. Cutting things up used to be the only way but mining saw a flood of cheap adapters on ebay, amazon, etc. I use a passive one in testing sometimes with no extra power and it works fine on cards like my GT710 which is designed to fit the 1x slot power envelope anyway.
I found this range input slider on PC Part Picker that allows you to filter on the number of slots the GPU uses. I wish I found it sooner. Even better, you can specify which power connectors you want. This is useful for me as I have already bought some CableMod cables so, switching up the power connectors renders them useless.
I noticed the Radeon WX5100 for about $350 with 8GB VRAM. But you can get a GT 730 on there for about $85 with 4GB VRAM.
Also wanted to point out that I couldn’t find any reports of the reset bug with the Radeon Pro WX series.
This is preset to filter to only cards with single slot width:
https://pcpartpicker.com/products/video-card/#a=0,1