Why need more than one TB3 port if TB3 hub is available?

Discussion in 'Buying Tips and Advice' started by hajime, Nov 11, 2018.

  1. hajime macrumors 601

    Joined:
    Jul 23, 2007
    #1
    Hi, given that one could connect to several TB3 devices at full speed using a dock, besides not needing to carry a dock, what is the advantage for having more than 1 TB3 on a laptop?
     
  2. maflynn Moderator

    maflynn

    Staff Member

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    Boston
    #2
    I suppose bandwidth. Instead of having multiple TB products on a single port you can spread the wealth if you. For example, have a monitor on one, external drive on another. I suppose in the end, it probably doesn't matter - I'm just thinking out loud here
     
  3. calliex macrumors member

    calliex

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    Aug 16, 2018
    #3
    For me I have not been able to find a reliable dock. They either get too hot, mess-up wifi, quit working, and are very exspensive according to all the reviews I have read. At a minimum I need to hook to an external monitor, plug in a thumb drive and charge the machine. That is three.
     
  4. hajime thread starter macrumors 601

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    Jul 23, 2007
    #4
    Is there a problem with the Caldigit's TS3+? It seems to receive high ratings.
     
  5. travelsheep macrumors 6502

    travelsheep

    Joined:
    May 30, 2013
    #5
    Nucleum by Kingston is supposedly the best hub.

    With that logic, why buy a Macbook, when you can buy a Mac mini? You just need to attach an external monitor, keyboard, mouse, and off you go! There's plenty of good USB-3 portable screens on Amazon, and you could buy a powerbrick and be mobile with the MacMini...
     
  6. hajime thread starter macrumors 601

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    Jul 23, 2007
    #6
    If I recall correctly, the TB3 ports of all MBP2018 can run independently at full speed. Is that right?
     
  7. maflynn Moderator

    maflynn

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    #7
    Yes
     
  8. techwarrior macrumors 6502a

    techwarrior

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    Colorado
    #8
    I think external monitor resolution may be higher when directly connected to a port on the Mac. When you have multiple devices connecting through a single TB3 port\hub, they share bandwidth. For multiple displays, getting each to be extended vs mirrored might depend on using multiple TB3 ports vs shared ports?

    I suspect folks are used to multiple ports and being restricted to one seems constraining. I also suspect the added cost of additional ports is negligible once you have one.
     
  9. theluggage macrumors 68040

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    Jul 29, 2011
    #9
    1. Not needing to carry a dock with a laptop (that boasts about how thin'n'light it is) is a biggie. Even having a boring old cheap-as-chips USB 3 drive, and your charger would mean that you needed a dock as well.
    2. there's no Thunderbolt dock with multiple Thunderbolt outputs - you can daisy-chain them, one after the other, but many cheaper/more compact Thunderbolt devices don't have a "through" port for chaining - or you might 'end' the chain by connecting a DisplayPort monitor or HDMI adapter. Also, on many docks, the TB 'out' socket is also the only 10Gbps USB 3.1g2 port - so if you need to connect a 3.1g2 device, that's no more thunderbolt devices on that dock. The other ports on the dock are usually 3.1g1 only (I think there's about 1 dock with a second 3.1g2 connection).
    3. Its a bit academic, but you can't connect several TB3 devices at full speed - the total 40Gbps has to be shared between those devices (although, frankly, that can go a long way - not many devices will hog the whole 40Gbps). I'm also not sure if the 40Gbps is per port or per controller - but in the 15" MBP, at least, each pair of ports has its own controller so you should get at least 2 sets of full bandwidth. Of course, the actual speeds you get are never as good as the figures!
    4. True thunderbolt docks are still quite expensive and bulky (and there's usually a big ugly wall-wart, too) - most of the cheaper mobile docks you see are USB-C docks and the important thing that some people miss about a USB-C hub is that it still only has the total bandwidth of a single, old school, USB 3.0 connection (and can't even manage that if you plug in a 4k@60Hz display, which knocks it down to USB2 speed). AFAIK, docks/hubs that use 3.1g2 or USB 3.2 (which puts 2 USB 3.1 streams down a USB-C cable) are still "watch this space".
    So, for example, if you bought a pair of these puppies:
    ...or even a pair of the cheaper T5 ones that use USB 3.1 gen 2 - there's no way of connecting them both at their full speed with just a single TB port and a hub.

    Now, who actually needs 4 x 40Gbps of bandwidth on a laptop (which would probably melt before it could actually process that amount of data) - especially if it means that all of your existing devices now need adapters or new cables - is another matter.
     
  10. mikehalloran macrumors 6502

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    Oct 14, 2018
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    The Sillie Con Valley
    #10
    No. There's only one way it matters, however.

    Not an issue.

    Though some models have 2 ports and others 4, there are only two busses on the latest MBP. Those with four ports have a built-in hub; the others do not.

    The clue is that you are restricted to a pair of 5K monitors, no matter which version—one per buss. If there were four TB3 busses, you could run four 5K monitors. BTW, you can run four TB3 4K monitors or a 5K on one buss and a pair of 4Ks on the other (same as an iMac Pro). The Apple support bulletin on this goes into greater detail.
     
  11. theluggage macrumors 68040

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    Jul 29, 2011
    #11
    No. 2-port Macs have 1 bus, 4 port Macs have 2 busses (2 ports per bus).

    Each pair of ports has its own Thunderbolt controller/bus - Macs with 2 ports have 1 controller, Macs with 4 ports have 2 controllers - you can see the differences in the teardowns of the MBP with touchbar or new Mac Mini (4 ports) and the MBP without touchbar (2 ports). Theres no such thing as a "Thunderbolt hub" (i.e. a device that takes 1 TB input and has 2 or more TB outputs) although you could picture the 2-port controller as incorporating something like that.

    I'm 95% sure that means that you can't run both ports in a pair at full 40Gbps speed* - but on a 4 port Mac you should be able to get full bandwidth on one port per pair.

    Yes, its currently only 1 5k display per controller/bus - because each controller/bus only has 2 DisplayPort streams and you need both of those to drive the current 5k display - so its one 5k per pair of ports. However, the 2-port Macs only have one bus so they can only drive 1 5k display... except that's moot because the only 2-port devices with GPUs that can handle two 5k displays are the 5k iMacs - and they use one of those internally.

    Do you have a link to that? Because it sounds like you're reading it wrong. There was a wrinkle with the 2016/2017 touchbar 13" MBPs (only) that, although they had 4 ports/2 controllers, the second controller was partly nobbled because the CPU didn't have enough PCIe lanes to go around (https://www.macrumors.com/2016/10/28/macbook-pro-tb3-reduced-pci-express-bandwidth/) - that's gone in the 2018 models.

    * Well, call that 100% sure but unable to find a simple, unambiguous link to back it up - but I was tired and tech journalists do so love using "unit soup" (oh my, we've already used Gbps once on this page, so lets quote the next one in GB/s and the next one in Wombats per fortnight...), manufacturers brag sheets obfuscate anything that might sound like a limitations, while tech documentation works in Wombats per fortnight for solid scientific reasons but kinda assumes you can convert in your head. :)
     
  12. mikehalloran macrumors 6502

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    #12
    Apple does not agree with you and neither do I
     
  13. IdentityCrisis, Nov 12, 2018
    Last edited: Nov 12, 2018

    IdentityCrisis Suspended

    Joined:
    Sep 9, 2018
    #13
    Did you try Caldigit TS3 Plus dock? I tried several and had issues with most except that one. This one worked the best for everything and never had a single issue.
    --- Post Merged, Nov 12, 2018 ---
    This is correct. You can not run 40gb from all 4 ports. Left side is 40gb shared, right side is 40gb shared. I've tested this and there was also an article that mentioned this a while back with eVGA units on the MBP's.
    --- Post Merged, Nov 12, 2018 ---
    Actually Apple does agree with him. You are reading it wrong and you are wrong.

    MBP 15" has two TB3 Controllers shared with two ports. Both controller supports 40gb per side of the laptop. You can't just get 40gb in one port and expect the controller to supply another 40gb on the other port. It's shared. If one port is eating up all the 40gb, there isn't much left for the other port. But if one port is using 20gb and the other 20gb, then they get the most they can from that controller. 20 per port. If you want 40gb, use one side for one and the other side for the other.
     

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