full image - Repost: For those considering a 2023 Mac Pro/Mac Studio Ultra (from Reddit.com, For those considering a 2023 Mac Pro/Mac Studio Ultra)
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When I started to research these two newest machines from Apple, I discovered that nowhere at all was it written how many PCI lanes these devices would support. It’s not published on the website, and in the many calls I made speaking with people in Apple sales, support and business sales, I got no info. Escalatong my question to Engineering didn’t work. So I wrote an email to Tim Cook, and one of his army of people emailed me back, and I asked him. He had no idea, but he promised to look into it for me. And eventually I got some answers. I didn’t get it in writing, presumably because if Apple hasn’t published it then it’s not official, but I kind of get that. They should have published it but they didn’t. Also, this info is corroborated by a white-hat hacker who is behind the push to get Linux running on M2’s, who claims he looked at the chips and the code and saw this for himself. Maybe it’s not true, maybe it is. But I have one of these machines and it’s not doing anything that would indicate it’s not true.Why is the number of PCIe lanes important? Because a lot of the things we attach to computers use PCIe lanes. PCIe lanes are not the same as PCIe slots. A slot is an internal connection where you attach a card, but a lane is a data connection to the CPU. Briefly, PCIe lanes can be thought of as reservations of bandwidth. Each lane on a Mac Pro represents a theoretical max of 2 Gigabytes (GB/sec) per second of bandwidth. On the highway from the CPU to the PCIe slots, the number of lanes available decides how much traffic (data) can go between the CPU and those slots. Slots usually have different numbers of lanes that they can accommodate.The Mac Pro has six slots available, of which two will accommodate 16 lanes each, and then four slots which will accommodate 8 lanes each. An example of a card that would use 16 lines would be the Sonnet 4X4 nvme card, which would allow you to mount four nvme drives upon it - and each drive would get the use of 4 PCIe 4.0 lanes, for a theoretical max of 8 GB/sec per drive. Consider that an external USB-C 3.2 Gen 2 drive does about 625 megabytes per second, so that is a huge speed boost. (Though there is no need for this in our business, if you made a huge RAID of those nvme drives, you’d get around 30GB/sec performance. Not 32, because there’s a little system overhead.)So - fill up the slots with drives on cards and you’re off, right? Yes, but also not exactly. The Mac Pro has those six slots that could accommodate a total of 64 lanes, but it only has a pool of 16 lanes to draw from. What?! It uses what’s called a PCIe switch to dynamically assign lanes where needed. But what if you have two 16-lane cards in there? (They would be either storage or networking cards, as the Mac Pro doesn’t support graphics cards. At all.) Why did they do this? Well, Apple are assuming you would never be using all 16 lanes from a card at once; and likely that will be the case often, if your libraries are spread out. If it has to allocate lanes to another drive on card #2, what would happen might be that a drive or two on card #1 might run at half-speed - which is a theoretical max of 4 GB/sec - still faster than anything you could do externally with that drive, and far beyond the speed requirements of sample streaming. So maybe not a problem. Alternatively, say you got 4 PCIe cards that held a single 4TB drive each and provided a max of 4 lanes to each one - that’s 16 TB of very high speed drives. And all of that is without plugging in an external drive.But what if you use an audio card? Say you use HDX or UAD or RME cards, or Dante cards. Audio cards usually use a lane or two, so you have to include those in your lane count. This would be a good time to dedicate a lane to the slot holding your audio card, and not include it in how many lanes available that you have.Now we get into Thunderbolt (TB). The TB specification allows for 4 PCIe lanes (remember those lanes are a data bandwidth amount) per port, but TB versions 3 and 4 only allow for 4 lanes of PCIe 3.0 bandwidth, not 4.0. In real-world terms, this amounts to around 2.8 GB/sec - absolutely sufficient for sample streaming. So since the Mac Pro has six ports that are independent from one another, that means a total of 24 lanes of PCIe via TB - and that doesn’t impact your internal lanes in the slightest. if you use a TB interface - I have a Lynx Aurora(n) 16x16 interface - it will use a single lane of bandwidth. It’s possible to use it on a chain of other devices - mine is connected to a TB hub that also has two displays and several USB devices on it. Do they interfere with each other? No, because just like the PCIe lane bandwidth is reserved, there’s also bandwidth reserved for video on each TB port. If you were to use, say, two 4-lane devices on a single TB port at the same time, each one would get two lanes. Which is around 1.4 GB/sec - still fast for most libraries.So what did I buy? The Mac Studio Ultra. The Pro is a cool machine in many ways, but I decided I didn’t need the card slots to have the speed I needed. 24 PCIe 3.0 lanes is fine for me. I have four WD SN850X 4TB nvme drives in Acasis cases, which will accommodate the libraries I have and more; and I have two TB hubs - one to connect iLoks and some other external storage to, and another to connect two iPads, my USB MIDI gear, two displays and the Lynx interface to - and that hub is connected to the Mac by a 15-meter optical Thunderbolt cable, which lets me keep the Mac in a machine closet with cooling and the noisier platter drives and so on. The Studio Ultra I got is the maxed out one, less the 8TB drive - four was enough, and faster to restore - but with more graphics cores and 192 GB of RAM. If I don’t use all 192 that’s fine - but my template is huge and I’d rather more than less, and I couldn’t upgrade it later. And I got the extra graphics cores because I’m making a long bet on graphics-core-based DSP. If VSL get MIR Pro 3D working with that, it would be a huge boost for me.The other reason that I went with the Studio Ultra instead of the Mac Pro is that the $3000 that I would’ve paid to have the Mac Pro ‘s PCIe slots amounts to 3/5 of an amazing custom PC that I could run as a satellite using Vienna Ensemble Pro that would do pretty much all of the other heavy lifting that I might want done, if it’s even necessary; and that machine, unlike the Mac, I could upgrade as much as I want.One can now see videos of tests of the Studio Ultra on YouTube. It’s shown that in Cubase it will achieve over 1,000 instances of Kontakt playing a scored cue, and in Logic, over 2,000. That really ought to do. And it’s possible now to do this with small buffer sizes, so most latency for playing appears to be a thing of the past. Certainly it’s nice to play instruments at 64 or 32 buffer, but one can set one’s buffers to 128 and pretty much leave them there. That’s what I’m talking about.So, hope this was useful. Off to use the darn thing.
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