Using 4k display as second display with 5k iMac

[theSeb]

I'm not sure there's much difference between "bumping" a cable and just pulling the plug on the iMac. Either way, I can't see how it would happen if you're even remotely careful, or, like I do - use a TwelveSouth Backpack!

FYI, I did test this back on a fresh install. I pulled the Thunderbolt cable out of the computer twice in a row, and it did no harm. The OS froze, I turned off the computer, plugged it back in, and booted back up.

And if it happens when your critical project is being saved? Anyway, let's get back on topic.

 

[WilliamG]

OK back on topic - can anyone confirm that we have two channels of 20Gbps via both Thunderbolt ports as per the previous post's description on how to see whether it does?

 

[Gav Mack]

Yeah, you crack me up. Talk about risk averse, ha. Anyway, I practice very sound backup techniques, even a total meltdown on a RAID 0 TB2 boot drive would be like an hour hiccup in my day. No reason to live in fear over that outcome. Anyway, lets try to get back on topic: More info from people with 5k iMacs about the TB2 situation.

I never used to be risk averse fella, 20 years in the business has made me that way. I got paid to pick up the pieces, but I warned it was a bad idea and I share the hard knocks with everyone here.

Personally I think you should setup with it as default, use the SSD in a tb enclosure for scratch perhaps and see how it goes first. 32 gb of ram with CS is rather good and if you've maxed out the spec with the BTO CPU and GPU it will fly..

Other option would be to get an engineer to get his heat gun out at a later date and fit a larger SSD blade..

 

[Gav Mack]

Now I've read back and looked at your uses I think even the default setup will be fine. It will drive another 4k fine via the specs.

I have similar uses as a hobby but slower kit a Mac pro 3,1 8 core with PCIe SSD's 32gb ram gtx 680 and use CS 6, quark (yes I know but I can rattle up in 5 mins what ID will take me an hour), a bit of FCPX and premiere and xmedia recode in bootcamp. Even this is not slow, I barely swap to disk cos I have the ram and a SSD scratch in SATA 2. You will have the benefit of the scratch for the power apps taking the I/O off the fusion at 4x my speed all round and I reckon you will be fine for now.

With a brand new bleeding edge system with overclocked proprietary interface driving the main panel, the possibility of EFI updates and bug fixes when they are all ironed out I say then go for it.

The usb comparison with the 6,1 is no surprise as usual from digilloyd - USB 3.0 is built in the chipset for the 5k but not for the 6,1 which has a pair of lanes going into a fresco chip. The 7,1 will have 3.0 baked in with the Haswell E chipset.

 

[scottomfg]

I emailed Lloyd at Mac Performance Guide with this question and his reply was:

Bus is separate for the display, does not eat up data bus.

LLoyd

I followed up asking if he could point me in the direction of any documentation and he replied that he'll post his own test but it'll be at least a week before he has time for it.

That said, Lloyd definitely knows his stuff and as far as I can see, this is the most authoritative answer to our query so far. Though, it's still far, far from certain.

It's killing me to have to hold off on my purchase, but this is so important (I plan on using this machine for several years as my primary work computer), I need to be certain that future expandability won't be extremely compromised.

 

[wmy5]

Two words: Flexibility and control. Whatever internal drive I order, effectively I will never have the ability to change it once ordered (I'm not tearing apart an iMac), and I will never have total control over how fast it is (I get whatever drive Apple gives me and that's it). Given these two factors, it seems like a bad way to invest money. Honestly, if I could order the iMac with no internal drive, that's what I'd do. But I don't get that option, so I'm choosing the one that gives me the most utility and requires the least monetary investment.

Using a 3TB Fusion drive for my internal storage is perfect for my usage: I have just over 1.5TB of photos, InDesign, Photoshop, Illustrator, and audio files I use for my creative work, but in any given month I'm only actively using about 1% of them, which does often include using files that are many years old. So, perfectly tailored to Fusion, which should keep what I'm actively working on in the SSD portion of the drive.

I want my boot drive to be pure SSD because I need it to always be the fastest I can reasonably make it. I already have a 6g 240 SSD, so I'll buy another for $140, stripe them in RAID 0, and have a super fast .5TB SSD boot drive. In addition to the above creative work, I also do a lot of coding and keep all those files in Dropbox, on the boot volume.

(The other two drives in my TB2 array will be a 4TB for TimeMachine and a 4TB for all my video files, this machine also will act as home media server)



I wasn't actually soliciting guesses, but actual knowledge. Many tests have shown RAID 0 external SSDs to be faster than Apple's internal SSDs, but I haven't seen anything that exactly matches my configuration (largely because the 5k iMac is so new), so I was soliciting some expert opinions.

Judging from the previous gen iMac, the internal SSD connected via PCIe gives about 700 W/R, which is incredible. But two 6g SSDs in RAID 0 should give at least around 775 W and 875 R (extrapolating from here), if not more. Just matching internal performance is enough for me though, as it's cheaper and gives me much more control and flexibility in the future—for instance, I'd always have the option of adding a third SSD drive to the RAID later and getting around 1,000 W/R.



It does indeed have two ports, and I would indeed use them both, not daisy chain. But both ports share the same bus, and this is where my knowledge becomes insufficient. I'm not sure what the capacity of the bus is, and if the display usage counts against it, or if it even matters. I was hoping someone who knows more than me about this can answer my question. On the new Mac Pros, the 6 TB2 ports are spread over 3 busses, so it is much less of an issue, but on the iMac, all we'll ever have is that one bus to use with TB2/DP.

I really don't think booting from a external drive is a good idea. It will hurt the performance. Yes you can get very high *throughput* via setting up RAID, etc. But what really matters is *latency* here. Accesses to a boot drive are mostly small size, highly random reads. High throughput cannot make any differences. Think about the extra latency incurred by two TB controllers, RAID controller, TB channel... What you get is actually a less responsive computer if you boot from an external drive.

 

[theSeb]

I emailed Lloyd at Mac Performance Guide with this question and his reply was:




I followed up asking if he could point me in the direction of any documentation and he replied that he'll post his own test but it'll be at least a week before he has time for it.

That said, Lloyd definitely knows his stuff and as far as I can see, this is the most authoritative answer to our query so far. Though, it's still far, far from certain.

It's killing me to have to hold off on my purchase, but this is so important (I plan on using this machine for several years as my primary work computer), I need to be certain that future expandability won't be extremely compromised.

https://thunderbolttechnology.net/tech/how-it-works

Reading the above tells me that he is right, if you do not daisy chain the display to the TB storage device and put each device on its own port for Thunderbolt 1 and non 4K displays. I believe that this is wrong when it comes to Thunderbolt 2 and 4K displays

I wish I could test this for you, but I only have slow drives in my Pegasus R4 and Lacie 2Big TB enclosures.

Here is anandtech's review of the Mac Pro 2013

Thunderbolt 2 bonds these channels together to enable 20Gbps in each direction. The total bi-directional bandwidth remains at 40Gbps, but a single device can now use the full 20Gbps. Storage performance should go up if you have enough drives/SSDs to saturate the interface, but more importantly you can now send 4K video over Thunderbolt. Given how big of a focus 4K support is for Apple this round, Thunderbolt 2 mates up nicely with the new Mac Pro.

So far I’ve been able to sustain 1.38GB/s of transfers (11Gbps) over Thunderbolt 2 on the Mac Pro. Due to overhead and PCIe 2.0 limits (16Gbps) you won’t be able to get much closer to the peak rates of Thunderbolt 2.

Here’s where the six Thunderbolt 2 and three TB2 controllers come into play. Although you can daisy chain a 4K display onto the back of a Thunderbolt 2 storage device, doing so will severely impact available write bandwidth to that device. Remember that there’s only 20Gbps available in each direction, and running a 3840 x 2160 24bpp display at 60Hz already uses over 14Gbps of bandwidth just for display. I measured less than 4Gbps of bandwidth (~480MB/s) available for writes to a Thunderbolt 2 device downstream from the Mac Pro if it had a 4K display plugged in to it. Read performance remained untouched since display data only flows from host to display, leaving a full 20Gbps available for reads. If you’re going to connect Thunderbolt 2 devices to the Mac Pro as well as a 4K display, you’ll want to make sure that they aren’t on the same chain.

Great, but this still does not explain and confirm what happens if we had the storage device and the 4K display plugged in the two ports of the same bus. I am going to ask people that know way more about this than I do.

 

[scottomfg]

Yeah Seb, I'm kind of surprised how little definitive information there is about this out there. For a machine like the 5k iMac, I feel like a lot of people are coming to it from a Mac Pro, and the biggest missing piece is expandability, so it becomes very important to know just how much you can push through those two ports. So, we'll see, hopefully.

 

[macmee]

Hi Scott,

Man.. this 5K display is out of the world.

The picture doesn't do it justice, the 4k Dell is out of focus, but it runs great. Verge is smooth as butter, nothing like the first gen retina MBP.

Sorry can't test TB2, don't have an enclosure, but rest assured your 4k + 5k display will be working great, and believe me, you can tell a difference from 4k to 5k.
Image

I've been searching for someone who's done a 4k off the 5k iMac since it came out, thanks for posting! Are you running it a 60Hz flawlessly? No lag at all? My rMBP 2014 is somewhat laggy with the 4k at 60Hz.

 

[EnderTW]

It runs great.

Granted I have maybe 5-6 apps running nothing intensive. I'm using the base model as well. Sites like the verge ios simulator etc look and run great scroll as fast as you can. The spaces transition is not smooth but I think that's Yosemite because it does a hiccup even without 4k.

 

[theSeb]

Yeah Seb, I'm kind of surprised how little definitive information there is about this out there. For a machine like the 5k iMac, I feel like a lot of people are coming to it from a Mac Pro, and the biggest missing piece is expandability, so it becomes very important to know just how much you can push through those two ports. So, we'll see, hopefully.

Good news, I believe that I have the answer and it makes perfect sense.

Each bus has a single TB2 controller which has a DP 1.2 input and a PCIe x4 bus interface on one side and a pair of TB2 ports on the other (20Gbps each). Daisy chaining obviously muxes both into one port and contention can occur if both are running near peak bandwidth.

Putting the display and PCIe device on separate ports (same bus) should eliminate contention and allow each to operate at full capacity.

What's not possible is running two 4K DP1.2 displays off one bus as there's only a single internal DP1.2 interface to the TB controller.

Similarly, running two devices that can both saturate a x4 PCIe bus on the same TB bus (controller) will likely create contention if both are used at the same time.

Looks like you're good to go with your plans.

 

[UNO]

Booting from lasie tb enclosure with 2 raid0 SSDs for 2 years now. No latency, high throughput, kids pull the cord every month or so- reboot and all the data is saved by OS X, backing up to external time capsule. The whole thing is much faster than internal SSDs I used before.

Added benefit is that I take this disk with me when traveling and boot right to my wife's rmbp. Also booted to others iMacs. So, I don't own a laptop anymore.

 

[scottomfg]

Booting from lasie tb enclosure with 2 raid0 SSDs for 2 years now. No latency, high throughput, kids pull the cord every month or so- reboot and all the data is saved by OS X, backing up to external time capsule. The whole thing is much faster than internal SSDs I used before.

Added benefit is that I take this disk with me when traveling and boot right to my wife's rmbp. Also booted to others iMacs. So, I don't own a laptop anymore.

UNO, thanks for fighting the good fight! I was getting worn out fighting against the bogeyman of RAID and external boot drives with this silly thing called a decade of experience From now on, I'll leave it up to you, ha.

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Good news, I believe that I have the answer and it makes perfect sense. Looks like you're good to go with your plans.

Seb! You're a superhero! I really hopes this holds true, would be fantastic news. I'm getting an itchy credit-card-number-typing-finger.

 

[theSeb]

Seb! You're a superhero! I really hopes this holds true, would be fantastic news. I'm getting an itchy credit-card-number-typing-finger.

I have to say this that question annoyed me, because it threw all of my understanding of TB out the window. I was confused about where the muxing of the PCIe data and DP signal happens and how.

 

[scottomfg]

The plot thickens, this just came in reply to an email I sent to Rob-ART at Barefeats:

The internal display connects directly to the PCIe bus. However, all external displays must share the TB2 single bus (2 port) bandwidth.

Apple says if you connect a 60Hz multi-stream transport (MST) 4K display to the 5K iMac, it supports one additional external Thunderbolt display.

This is discussed on this support page:
http://support.apple.com/kb/ht5219

However, if you are planning to use a RAID 0 storage that uses most or all of that 1375MB/s bandwidth, then adding a 4K display may not be a viable idea.

Rob

The plot thickens . . . people in the know, and experienced users, are on both sides of the speculation, both with what appears to be sound reasoning. Still have yet to see anyone do an actual test and put this issue to rest. I ordered mine this weekend, but currently says 21 days to delivery. Hopefully this gets sorted by then.

 

[DaveFP56]

How about Lightroom ?

I don't have the technical knowledge you folks have so I am wondering if anyone here can answer this:

I am a photographer that would like to be able to hook this 5k iMac to the upcoming 4k Eizo display.

I want to use it in conjunction with Lightroom; a known resource hog.

Making the assumption that I bought a top-level spec machine would this be a speedy/laggy combo?

Any insights much appreciated.

 

[scottomfg]

Got my shipping notice this morning. iMac set to arrive on Monday, all my extras (array, drives, 4k display, etc) should be here by Wednesday. If no one has done the necessary benchmarks to figure this stuff out by then, I will do some basic benchmarks and answer this finally.

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I don't have the technical knowledge you folks have so I am wondering if anyone here can answer this:

I am a photographer that would like to be able to hook this 5k iMac to the upcoming 4k Eizo display.

I want to use it in conjunction with Lightroom; a known resource hog.

Making the assumption that I bought a top-level spec machine would this be a speedy/laggy combo?

Any insights much appreciated.

It will be a very speedy combo, just be sure you option your iMac with the faster processor and SSD drive, and get at least 16gb of RAM (I'd recommend 32gb, only $270 from Crucial via Amazon). 2d graphics, like Lightroom, won't tax the video card even with those two retina displays, and for an app that isn't super hyper-threaded, like Lightroom, nearly all tasks will be faster on this iMac than on any Mac Pro.

 

[mintakax]

Got my shipping notice this morning. iMac set to arrive on Monday, all my extras (array, drives, 4k display, etc) should be here by Wednesday. If no one has done the necessary benchmarks to figure this stuff out by then, I will do some basic benchmarks and answer this finally.

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It will be a very speedy combo, just be sure you option your iMac with the faster processor and SSD drive, and get at least 16gb of RAM (I'd recommend 32gb, only $270 from Crucial via Amazon). 2d graphics, like Lightroom, won't tax the video card even with those two retina displays, and for an app that isn't super hyper-threaded, like Lightroom, nearly all tasks will be faster on this iMac than on any Mac Pro.

That's a pretty broad statement, "nearly all tasks" and "any Mac Pro ".
One I doubt you will be able to reliably demonstrate.

 

[macmee]

Not to add another nail to the coffin, but I have a 4k monitor running at 60hz off my riMac and whilst it's not terribly lagging, there is some glittering going on. I'm very convinced that if you were to throw any other high bandwidth devices on the bus that it might be incredibly slow.

 

[scottomfg]

That's a pretty broad statement, "nearly all tasks" and "any Mac Pro ".
One I doubt you will be able to reliably demonstrate.

I don't think I need to reliably demonstrate anything to prove my point. Every benchmark I've seen shows that, CORE FOR CORE, the 4Ghz 5k iMac cpu is faster than those found in the current Mac Pros. So as long as what you are doing doesn't use more than 4 cores, or farm out work to the GPU, the iMac will be faster. Which is all I said.

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Not to add another nail to the coffin, but I have a 4k monitor running at 60hz off my riMac and whilst it's not terribly lagging, there is some glittering going on. I'm very convinced that if you were to throw any other high bandwidth devices on the bus that it might be incredibly slow.

That's not a nail in any coffin that we're discussing. Any 'gittering' you see is not from TB2 or DP 1.2 bottlenecks, but from GPU limitations (a 5k and 4k display together is a lot of pixels to drive). And, even more to the point, the only real question of this thread is: does the DP 1.2 signal going to the 4k display eat into the 20Gbps available on the TB2 bus or is it somehow independent of the TB2 bus.

Experts have weighed in on both sides, so we're just waiting for some real world tests to find out the truth.

 

[mintakax]

I don't think I need to reliably demonstrate anything to prove my point. Every benchmark I've seen shows that, CORE FOR CORE, the 4Ghz 5k iMac cpu is faster than those found in the current Mac Pros. So as long as what you are doing doesn't use more than 4 cores, or farm out work to the GPU, the iMac will be faster. Which is all I said.

Sorry, I missed that qualification in your original statement.
I have apps that use all 8 cores of my nMP. I doubt I would be happy with a new iMac .
Today my wife's beefy 5K iMac is arriving so it will be interesting to test some things. I seriously doubt that FCPX 4K editing will be as fast nor will a lot of the scientific data analysis that I do on my nMP.

 

[scottomfg]

Sorry, I missed that qualification in your original statement.
I have apps that use all 8 cores of my nMP. I doubt I would be happy with a new iMac .
Today my wife's beefy 5K iMac is arriving so it will be interesting to test some things. I seriously doubt that FCPX 4K editing will be as fast nor will a lot of the scientific data analysis that I do on my nMP.

Yep, I totally agree. No doubt in tasks that utilize all available cores, the nMP with more than 4 cores have an unbeatable advantage. These days software, and correspondingly, hardware, are so specialized that there really isn't a 'best' machine any more—it really comes down to how you'll use it. For photographers, it's hard to argue against the 5k iMac, for videographers, it's hard to argue against a crazy nMP (budget concerns not withstanding, of course).

 

[medazinol]

I can confirm that the new Retina iMac works perfectly with the Samsung U28D590 28" 4K display using Yosemite.

I just used a display port to mini display port cable to hook them up. The displays control panel shows the D590 as if it was a retina display including the scaled options and rotation drop down.
Refresh rate seems to be 60z and scrolling is buttery smooth. Mission control is laggy but that seems to be a universal bug in Yosemite across the board.

I've attached a screen shot of the monitor as proof.

Larger format:

 

[scottomfg]

Not too far away now.

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I can confirm that the new Retina iMac works perfectly with the Samsung U28D590 28" 4K display using Yosemite.

I just used a display port to mini display port cable to hook them up. The displays control panel shows the D590 as if it was a retina display including the scaled options and rotation drop down.
Refresh rate seems to be 60z and scrolling is buttery smooth.

That's awesome, congrats!

 

[scottomfg]

Everyone has arrived. Now to see how far I get tonight before I pass out. I'm using the SSD that is the current boot drive on my Mac Pro as half of the SSD RAID in the ThunderBay (which I will need to do the test to actually figure all this out) so I have a lot of backing up and copying to do first. But it's still possible I'll get some tests done tonight.