When building out a DaVinci Resolve color suite, there might be some things and pieces of gear that you may not think about. What are these other elements you need to incorporate? In this video, authors Robbie Carman and Patrick Inhofer discuss what a GPU expander is and why you may want to include one in your DaVinci Resolve hardware setup.
- Earlier we talked about GPU's and how important they are when selecting a GPU, How DaVinci Resolve loves having multiple GPU's, it'll take advantage of them. But we kind of glossed over the notion of how do you add multiple GPU cards to your system if you can't fit them inside your computers, so what are our options? - Well, we did say that some motherboards and some systems, when they have the ability to not share bandwidth, and provide full 16 times lane PCI slots.
I mentioned my HP Z840 which allows me to do that, and some other motherboards will allow you to do that. Well then yeah, you can fit one, two, maybe three, even four cards in one of those motherboards if you have nothing else to put in there, but when you have a motherboard that shares bandwidth across slots or slots are slowed down when you put another GPU in, it can be challenging. And, going back to the Black Magic configuration guide, one thing that Black Magic suggests, and pretty much any platform, MAC, Windows as well as Linux, is something called a GPU expander.
So, what is a GPU expander? Well, as it's name implies, it allows you to expand the amount of GPU's that you can use in your system. Now it's not just GPU's, think about it as a PCI expander. The way that these boxes work is that you have a host bus card that goes in your computer, another PCI card, this is a 16 time card. You can find these cards in PCI gen two and PCI gen three. These day I would suggest getting the PCI gen three.
That card then attaches to this external box, the external box has a number of PCI slots in it. Now the thing about the box is it has it's own power, and all of the lanes are full bandwidth. Now you're saying to yourself, Rob, how can that possibly, how can that possibly work when I have, you know, four or five cards in a box, how does it share it over one PCI connection back of the box? - I don't know How does it do that, Rob? - Magic, no, seriously there's a lot when it comes to GPU's, without getting into very boring details about it, the throughput is sort of moderated by your host computer or by the software itself.
Unless you have, you know, 25 GPU's on a single slot, which you cannot do, you're not going to saturate that pipe. Resolve, the way it works, is able to intelligently handle the traffic going back and forth between those. Now, these are available from several companies. Cubix is one very popular manufacturer. They make a desktop version which is just a square box, they also make a rackmount version. The rackmount ones you're going to be able to get more cards into. And there's another company called Magma, Magma makes a couple different styles of these too, both desktop as well as rackmount.
- Now the pricing on these is about the same depending between the two manufacturers, they'll start at around $3,000 and then they'll work their way up. These are boxes and expander cards that can really handle more than two, right? You can find single slots and double slots. - Yeah, these are not just like the Thunderbolt expanders that you would need for your iMac to put in a fiber channel card. These are much bigger devices because they have their own power. - And their own fans. - Right, they are not exactly all that well suited to kind of just have on the desk next to you.
- Yeah, I've had one of those underneath my desk and it sounds like you've got a vacuum cleaner down there so they tend to be a little noisy because they're really designed to be put into a machine room, that's their intention, so they're not really all that concerned about noise, they're not really designed for noise reduction. - Right, and it's not just GPU's, if you have the need to put in other cards in that expansion box that's possible as well. Recently I scaled back on the number of GPU's I was using in my resolve system because the GPU's have gotten so good, that it was a case of diminishing returns, So I put, a Sata card in that box as well, so when a client walks in with a, you know, older drive, I can just plug that in as well.
- I think you could even put in a DeckLink card in there as well, right? - Sure, absolutely. - And run it through there. Now one point that you just made, that I think we should talk about a little bit, as you think about adding an expander box, is the case of diminishing returns. Like, how many GPU's is overkill? - So, this is a really kind of hot topic, because I'm a GPU addict, that I look into all the time. Now DaVinci Resolve itself does not limit the amount of GPU's that you can use. The Resolve team has told us, "Hey, if you can throw a GPUs, and it does Cuda, "or it does OpenCL, we'll use it." Right, but OS's will have different considerations.
For example, Apple over the past few years, has kind of flip-flopped. Some versions of OS you could use two or three GPU's, some versions you could use four GPU's. Other times, I was in the middle of a project once and somehow my machine updated, and I lost two of my GPU's, right. So it's going to be a little bit OS dependent, but you're right about the case of diminishing returns. At a certain point, adding another card, yup, that's going to kind of really amp things up, adding a third, yup, fourth card, eh. - You really need to be working at really large file sizes, you need to be working stereo, and at that point, when you're pulling two streams for stereo workflows, that's really when you get beyond three GPU's, that's where those addition GPU's really start to sing.
- And this is something that also, it used to be that the GPU expander chassis was almost a requirement, because the cards weren't nearly as fast, that you did have to use three, four of em at a time. These days the cards are getting so fast even for UHD work, that two-card is plenty for a lot of scenarios. But as you mentioned, if you're doing, you know, high-frame-rate 8K stereoscopic, then yeah, you're going to have to expand. But GPU expanders, they do offer you that ability, they're pretty expensive, but when you need to get that expansion so you can get the most power on you system, they're the only way to go.
- Understanding Linux, Mac, and Windows Resolve systems
- Key hardware components: CPU, RAM, and GPU
- Video reference monitors
- Control surfaces
- Hardware accessories for color correction