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External GPU for Octane - Connected to imac - possible or not?

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Hi everybody,

I’m looking for some advice on a new mac purchase.

I need a mac primarily for design, editing and 2D/3D motion graphics but also everyday use.

I also need a monitor as I’ve been using a MBP retina up to now.

So I’m thinking of getting the following:

imac retina

4.0GHz Quad Core i7 (turbo boost up to 4.4Ghz)

32GB ram

with AMD Radeon R9 M295X 4GB GDDR5

Which will be fine for most tasks (I’ll keep my laptop for team render) but no Nvidia = no CUDA.

I have a big shopping list of things I’m continuing to learn but pretty soon I’m going to want to try GPU rendering, almost certainly using Octane as it seems to have the biggest take-up of any GPU based renderer.

I know I probably should get a PC at this stage, but I’m kicking and screaming against it for many reasons which I won’t detail here.

My question is once I reach that point and assuming Open CL take up is still some time away will I be able to connect an external chassis, power unit and a 2-3 Nvidia/cuda cards, connected to my iMac retina over Thunderbolt 2?

At this point my limited understanding melts my puny brain. I have all kinds of concerns about cooling/blowing up expensive graphics cards and I have no idea if this is even possible over Thunderbolt 2. Maybe the data will be too much to handle through a single thunderbolt connection. Will the iMac recognise the cards connected in this way, will Octane be as responsive as if it was connected over PCI? etc etc…

I’m sure a lot of freelancers/small studios are also pondering the future of GPU rendering using macs so any help is really appreciated before I waste my dollars on a grand plan that won’t pan out. Like I said, I know a Windows PC makes the most sense but I’m looking for a mac only solution.

Many thanks!


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Im a windows guy, so I don't know too the specifics too well, but have read its possible. I know thunderbolt can only handle 1 or 2 per thunderbolt connection depending which the spec the port is. The speed is theoretically the exact same as a PCI connection. Thunderbolt is essentially external PCI.


Someone with more mac experience will have to advise whether SLI works on a mac or not.

My understanding is that you have to get very specific cards that os x will work with. If that is true, options may be limited as Apple becomes more married to AMD, which may be a much larger problem in the future when its time to upgrade the card. Maybe OpenCL will be more standard by then, but its a gamble.


The primary issue I see is in how the video cards would receive power. All of our cards (titans & 680s) each have direct PEG8+PEG6 connections required, which come off the internal PSU. This all amounts to a needing a fairly large box to house everything.

I have all kinds of concerns about cooling/blowing up expensive graphics cards........

You have to try really, really hard to blow something up. The only way these things completely fry is by throwing a ton of extra voltage at the card or cpu as an overclocking measure. Since you are on a mac, you don't really even have the option to. If anything overheats or has any type of power irregularity, the computer usually just does an emergency shut-off to avoid damaging hardware.

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Hi, i`m also curios about possibility to add external GPU`s to mac. I`m using Blender for 3D and i`ve heard there is guys who render with External GPU`s same as PC guys. The bandwidth needed for GPU rendering isn`t that high as needed for games, so almost no performance loss. However i think it`s supertricky solution , becouse Apple doesn`t officially support any of those nvidia GPUS and updates can fuck up something. If you`re willing to risk , i think you just should buy this device -> http://eshop.macsales.com/shop/Thunderbolt/PCIe_Chassis/Mercury_Helios_2 , i think you can also ask questions to those guys, who sell these chassis. At this moment i`m just sticking to PC. Dunno what Apple is thinking by not giving GPU options for motion designers , 3d artists :/ If you change your mind towards PC, check this thread, it has some nice info : http://mograph.net/board/index.php?showtopic=29763

Edited by Agris

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Perfect. There is also this shorter/newer thread: http://render.otoy.com/forum/viewtopic.php?f=9&t=44582

So no OSX version can handle over 5 GPUs right now.


I've posted a bit about this, so I don't want to repeat too much here (search my threads)...basically what you would pay for a mac + enclosures would buy you the same PC/monitor/GPUS and an additional Titan Z.


I'd take another 5700 cuda cores over OSX any day...maybe that's just me.

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while the external enclosure is very promising, it's so expensive as to be pointless.

I'm with jblessing on this one, grab a PC with enough room to add 2 (possibly 3) decent GPUs.


IMO Octane for C4D is still flaky at best (with yosemite at least - I've had a few crashes in the last couple of days) and if you can handle using win7/8 then it will be better for your sanity in the long run. BTW I have no idea what kind of instability you'll be introducing by mixing ATI and nvidia drivers, particularly when you want to run the nvidias externally.

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thanks everyone for the replies.


Despite my wishes to stay with Mac it does seem that PC makes the most sense.

My only issue with this (other than finding equivalents for software etc - thanks for the link!) is that I haven't built a PC for 15 years and really don't have a clue when it comes to picking parts. In fact I find the whole process pretty intimidating, mainly because I can't really afford to buy the wrong thing!


What would you suggest?


My budget is pretty much the cost of a new fully specced imac retina (top CPU, upgraded GFX card/32gb independently sourced ram)


Imac retina:

4.0ghz QUAD Core Intel i7

8 GB Ram default

1 TB storage drive

4GB Radeon R9 M295X 4GB GDDR5

$3600 (Australian dollars)

Cost of extra ram: $495 32GB (Australian dollars)

Total cost: 4095 (Australian dollars)

Is there a PC build you could recommend for this budget?

The monitor and operating system would need to be included in that too - 27" or near enough.

Expandability would be nice if I can find the $$$ for extra GPU.

CPU still important as would need to work on some projects in C4D without Octane.

I'm a freelancer so this machine is geared towards working efficiently and spending less time rendering.

Really appreciate any input. I found a few threads from 2013 but are obviously outdated. Hopefully others looking at jumping ship will find this info useful.






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1 Intel Core i7-5960X Haswell-E 8-Core 3.0GHz LGA 2011-v3 140W Desktop Processor BX80648I75960X

Item #: N82E16819117404

Return Policy: CPU Replacement Only Return Policy $1,049.99 1 ASUS RAMPAGE V EXTREME LGA 2011-v3 Intel X99 SATA 6Gb/s USB 3.0 Extended ATX Intel Motherboard

Item #: N82E16813132262

Return Policy: Limited Replacement Only Return Policy -$20.00 Instant $499.99

$479.99 1 G.SKILL Ripjaws 4 series 64GB (8 x 8GB) 288-Pin DDR4 SDRAM DDR4 2800 (PC4-22400) Intel X99 Desktop Memory Model F4-2800C15Q2-64GRK

Item #: N82E16820231820

Return Policy: Memory Standard Return Policy $999.99 2 Crucial MX100 CT256MX100SSD1 2.5" 256GB SATA III MLC Internal Solid State Drive (SSD)

Item #: N82E16820148820

Return Policy: Limited Replacement Only Return Policy -$20.00 Instant $119.99

$199.98 1 LIAN LI PC-A75 Black Aluminum ATX Full Tower Computer Case

Item #: N82E16811112387

Return Policy: Standard Return Policy -$10.00 Instant $189.99

$179.99 2 EVGA 04G-P4-2983-KR GeForce GTX 980 4GB 256-Bit GDDR5 PCI Express 3.0 x16 SLI Support Video Card

Item #: N82E16814487079

Return Policy: VGA Replacement Only Return Policy -$5.00 Instant $1,139.98

$1,129.98 1 SILVERSTONE ST1500-GS 1500W 80 PLUS GOLD Certified Active PFC Power Supply

Item #: N82E16817256110

Return Policy: Standard Return Policy -$30.00 Instant $349.99



Monitor = http://www.monoprice.com/Product?c_id=113&cp_id=11307&cs_id=1130703&p_id=10489&seq=1&format=2 $460




This is a fairly top of the line, maxing out everything PC with everything you need. I forgot to add a cooling system, which I highly recommend you do with the GPUs heating things up. Total with monitor comes to about $4900 USD which is a bit over budget, but not by much.


There is plenty of wiggle room here if you want to save money. Everything in the list made of the latest & greatest components available right now.

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AromaKat is on the right track.


The GPU workstation I am currently using is:


5960x i7

Asus x99 WS-E motherboard

64GB Corsiar LPX RAM

2x Samsung SSDs (OS and cache)

1x 1TB Western Digital drive (project files)

external raids (existing)

Corsair 780t case

EVGA 1600w PSU

Corsair H100i CPU cooler

2x Titan Z


If you don't plan on every putting 4 GPUS in, there is no need for the 1500W PSU. 1200w would be plenty for only 2-3 GPUs and that i7 OC'ed.


If you only do 32GB of RAM and 2 x 980 GTX GPUs, you would be in range of your budget. Maybe loose the 5960x CPU for a 5930K to save $500. I'm a big fan of the ASUS WS-E and Rampage boards, but they make cheaper ones that are good if you don't want room for 4 GPUs. EVGA also has a good board (x99 classified) that we have 4 x Titan blacks running on now that has been great too. Right now we are still using our 27" Apple displays, so I can't recommend anything there. I hear Dell and LG have some good monitors for around $500-700.


Octane has been a lot more stable on this Win 8.1 PC with multiple GPUs than it ever was with the old Mac Pro with a GTX 680. Having at least 2 GPUs really helps when working in it. Octane still needs to grow in stability, but the problems are worth the performance...just keep auto-save on :)

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is where i used to buy computer parts if you are building it yourself. \

if you live in sydney, there is a computer shop with really nice staff at bondi junction



ziplink computers.

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Many thanks to everyone!

So Ive started speccing out this new Octane readymachine. Heres what I have so far.

It’s going to cost more than I was hoping but I would like to get as close to $4500 (AUD) as possible. I realise certain things will probably need to be sacrificed.

Total ($AUD) excluding SSD HD, regular HD, Motherboard, Monitor and PSU = 3129

So I’m getting close to my Max of $4500 AUD.

I’ve seen cheaper SSD and regular drives on CPL but not sure if they would be any good?

I really have absolutely no clue at all about what I need from a motherboard, PSU either.

And of course I’ll need a pretty decent monitor too for my work, preferably 27” or close enough.

Ideally 4K but Im probably dreaming haha.

I’ve read that the 780 Strix GPU is good as it has 6gb Ram. My next choice if I can’t get hold of them would be 'GPU X 1 - Evga 04G-P4-2986-Kr Nvidia Geforce Gtx 980 Ftw Graphic Card 4Gb - CPL ($820)'

What do you think of this build? - I read about the DDR4 ram but its pushing the price up. So Im hoping I can get by with DDR3. I realise the storage isnt massive but I can always increase that next year.

Ill be buying from CPL Online most likely. Id love to know your thoughts so I don’t buy a stinker. Thanks for all the advice so far, its massively appreciated!

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Hard drives - You will need a system SSD (make sure you get sata III / 6gbps SSDs), and another SSD dedicated to being your cache. For storing projects on and working off of, you will want a good RAID array, which you can have internal and controlled by your motherboard. I highly recommend making a RAID 10 array. You get the speed of a raid 0 with the redundancy of a RAID 1. DO NOT RAID 5!!!! RAID 1 or RAID 10 are really the only options, with raid 10 being best if you are working with large media files. So.. You will need 4 - 8 drives. RAID 1 or RAID 10 will cut your storage amount in half. At the very least, get 2 drives and raid 1.


Motherboard - Im personally a huge fan of Rampage boards but honestly haven't really shopped for one in a while. Be weary of anything under $400 - $450. If you can get a motherboard with thunderbolt support, it will be a huge help for when you get a drive from a Mac person. I just learned the hard way there is absolutely no way to use an adapter for use in that direction and ended up having to fork over a lot of money for a weak-ass iMac just so I can read dumbass thunderbolt drives. So pissed. Anyway... The primary thing to look for in a motherboard is expandability. The more PCI slots, USB ports, memory slots, etc the better. Try to get a board that has a TON of PCI. Preferrably all full sized x16 if possible, especially if you plan on throwing more video cards in over time.


PSU - with 2 video cards and a lot of hard drives, you will want around 1500 watt. Just add up power consumption of everything and add healthy amount of overhead. Don't go cheap on the PSU. I have had 4 or 5 cheap PSUs catch fire.

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