Hi!

I don't know a ton about how VRAM sharing works in general, so maybe this is a bad question.

If I have two NVIDIA RTX 4090s with 24 GB of VRAM each, could that increase the effective VRAM to 48 GB when rendering in Karma?

AnsonSavage
Hi!

I don't know a ton about how VRAM sharing works in general, so maybe this is a bad question.

If I have two NVIDIA RTX 4090s with 24 GB of VRAM each, could that increase the effective VRAM to 48 GB when rendering in Karma?

Maybe I am wrong , but I think only Redshift renderer can sharing VRAM between multi GPU right now

The cards would need to be connected with a nvlink to share memory. Sadly Nvidia have been removing the nvlink connection from the gaming cards lately

happybabywzy

AnsonSavage
Hi!

I don't know a ton about how VRAM sharing works in general, so maybe this is a bad question.

If I have two NVIDIA RTX 4090s with 24 GB of VRAM each, could that increase the effective VRAM to 48 GB when rendering in Karma?

Maybe I am wrong , but I think only Redshift renderer can sharing VRAM between multi GPU right now

Okay, cool! IDK if this is outdated, but I just found this that suggests that Redshift isn't able to do this currently...?

https://support.maxon.net/hc/en-us/articles/1500006456701-When-Redshift-uses-multiple-GPUs-is-their-memory-combined- [support.maxon.net]

NVLink still works, some more info here.

https://support.maxon.net/hc/en-us/articles/1500006456521 [support.maxon.net]

"Finally, it should be noted that the VRAM of multiple GPUs is not combined together! I.e. if you have an 8GB GPU and an 11GB GPU installed on your system, these do not add up to 19GB! Each GPU can only use it’s own VRAM, unless you link them together with NVLink. NVLink is an NVidia technology (so it’s only supported on NVidia GPUs) which can “bridge” two GPUs together so that they can share each other’s memory. This comes at a performance penalty which might or might not be considerable in some cases. Redshift automatically detects and uses NVLink, if present."


Strange they did not mentioned it on the link you sent.

Heileif
NVLink still works, some more info here.

https://support.maxon.net/hc/en-us/articles/1500006456521 [support.maxon.net]

"Finally, it should be noted that the VRAM of multiple GPUs is not combined together! I.e. if you have an 8GB GPU and an 11GB GPU installed on your system, these do not add up to 19GB! Each GPU can only use it’s own VRAM, unless you link them together with NVLink. NVLink is an NVidia technology (so it’s only supported on NVidia GPUs) which can “bridge” two GPUs together so that they can share each other’s memory. This comes at a performance penalty which might or might not be considerable in some cases. Redshift automatically detects and uses NVLink, if present."


Strange they did not mentioned it on the link you sent.

Oh, cool! From what I read, NVIDIA doesn't support NVLink on 4090s anymore, is that right?

AnsonSavage

Heileif
NVLink still works, some more info here.

https://support.maxon.net/hc/en-us/articles/1500006456521 [support.maxon.net]

"Finally, it should be noted that the VRAM of multiple GPUs is not combined together! I.e. if you have an 8GB GPU and an 11GB GPU installed on your system, these do not add up to 19GB! Each GPU can only use it’s own VRAM, unless you link them together with NVLink. NVLink is an NVidia technology (so it’s only supported on NVidia GPUs) which can “bridge” two GPUs together so that they can share each other’s memory. This comes at a performance penalty which might or might not be considerable in some cases. Redshift automatically detects and uses NVLink, if present."


Strange they did not mentioned it on the link you sent.

Oh, cool! From what I read, NVIDIA doesn't support NVLink on 4090s anymore, is that right?

Yes

I asked in March, the answer is no, there will be no NVlink support for Karma!

https://www.sidefx.com/forum/topic/89388/ [www.sidefx.com]