# How many externals to a USB hub

• When mining Burst, How many external drives can reliably and speedily(yes it's a word) go onto a powered USB 3.0 hub?

I don't want to buy a 10-port 3.0 powered hub if the answer is something like only 3 externals

• USB3 is 5gbps = 625 MB/s (megabytes per second) Calculate how many drives are on one port "one port can equal to a hub to one port" and how fast they are in Megabytes each, same goes for below. Now if you bought USB3SS card and SS enclosers = 10 Gbps, also called USB 3.1 Gen 2 = 1250 MB/s (megabytes per second).

• I have 5 on a powered USB hub and really don't see any performance hit. But as @Hitti2 points out, there is only so much bandwidth, so I am sure there is a point where performance will degrade.

The real pros can probably tell us the preferred maximum per USB card/interface (I have 2 usb 3.0 cards installed in my system 3 drives on one, and 6 total on the other)

• It depends on several factors, but generally, in order to get the best possible read times from my Seagate backup plus 8TB drives, I don't wish to connect more than three in a USB 3 hub. The hub itself does not need to be powered if your drives have their own external power supply.

When mining multiple drives, you will most likely reach a bottleneck in the bandwidth of your USB 3 host controller. Theoretical max speed of one USB 3.1 gen 1 host controller is 625 MB/s, but I have been told 320 MB/s is a more likely number. When we mine our plots, we only need to read one scoop out of 4096 each round, which represents 0.025 % of the total size of plots. So, if we have 50 TB of plots (50 000 000 MB), we only need to read 50 000 000 x 0.00025 = 12 500 MB in one round.

12 500 MB per round / 320 MB/s (controller likely speed) = 39.0625 seconds. Total round time of about 39 seconds can be improved by dividing the HDDs onto multiple USB 3 host controllers using a dedicated USB 3 multi controller card (such as this one: http://www.sonnettech.com/product/allegroprousb3pcie.html). Read speed will also be impacted by the read speed of the HDDs themselves, as well as CPU/GPU/motherboard.

Conclusion: If you don't care about fastest possible read times, buy a 10-port USB 3 hub. If you do care, go with small hubs so that you can get the most out of your USB 3 host controller, and preferably get hold of one of those multi controller cards I linked to.

• @Propagandalf
Good point, all my externals have their own supply

I think I'll get an unpowered 10port, an only connect 3 or 4 at first and see how much of a difference there is each time I add one

My laptop has four 3.0 ports, so I plan to "max" them out before I buy a dedicated machine just for BURST-ing

• @mrgoldy Sounds like a good plan! Since you're on a laptop chances are big that all your four USB 3 ports route back to the same USB 3 host controller, so basically they're the same as a hub. Unfortunately, that card I linked to is meant for desktops, but I think there are ways of upgrading laptops with more host controllers as well.

• @Propagandalf

It looks like I have 2 Host Controllers, maybe 3?
Or is the 3.0 the only one? and the others above it are 2.0?

• @mrgoldy The enhanced controllers are USB 2, whereas the extensible is USB 3 :) You should be able to tell the diffence when you look at the ports. USB 3 ports are usually blue colour, or red, like on my laptop.

• @Propagandalf
all 4 of 4 ports are blue, that's why I'm a little confused
ASUS ROG G750JW in case you're wondering

• @mrgoldy Hmm... strange, maybe there are some internal USB 2 connectors for legacy compatibility or something like that, that you can only access by opening it up. Or maybe they are connected to some other bus through a different type of connection on your laptop. I really couldn't tell you, but you will notice a big difference in speed from USB 2 to USB 3 when mining. :)

• This post is deleted!

• It depends on several factors, but generally, in order to get the best possible read times from my Seagate backup plus 8TB drives, I don't wish to connect more than three in a USB 3 hub. The hub itself does not need to be powered if your drives have their own external power supply.

When mining multiple drives, you will most likely reach a bottleneck in the bandwidth of your USB 3 host controller. Theoretical max speed of one USB 3.1 gen 1 host controller is 625 MB/s, but I have been told 320 MB/s is a more likely number. When we mine our plots, we only need to read one scoop out of 4096 each round, which represents 0.025 % of the total size of plots. So, if we have 50 TB of plots (50 000 000 MB), we only need to read 50 000 000 x 0.00025 = 12 500 MB in one round.

12 500 MB per round / 320 MB/s (controller likely speed) = 39.0625 seconds. Total round time of about 39 seconds can be improved by dividing the HDDs onto multiple USB 3 host controllers using a dedicated USB 3 multi controller card (such as this one: http://www.sonnettech.com/product/allegroprousb3pcie.html). Read speed will also be impacted by the read speed of the HDDs themselves, as well as CPU/GPU/motherboard.

Conclusion: If you don't care about fastest possible read times, buy a 10-port USB 3 hub. If you do care, go with small hubs so that you can get the most out of your USB 3 host controller, and preferably get hold of one of those multi controller cards I linked to.

Thanks. I use the same drives as you and was going to buy a 50 dollar 10 port powered hub. Still might as it had good reviews but might be overkill link. I have 6 USB 3.0 ports but am currently plotting my fifth drive ;)

• @Propagandalf I have 5 superspeed and one eXtensible so I have 6 USB3.0 controllers correct? Makes sense since I have 6 blue USB ports.

• @Propagandalf
all 4 of 4 ports are blue, that's why I'm a little confused
ASUS ROG G750JW in case you're wondering

Most controllers with 3.0 capability will show the 2.0 ghost ports in device manager or a usb tree viewer for the backward compatibility for 2.0 devices.

• currently run 7 externals through a hub and takes 27 seconds to read almost 30tb around 300 Mb/s

• @Propagandalf I have 5 superspeed and one eXtensible so I have 6 USB3.0 controllers correct? Makes sense since I have 6 blue USB ports.

It is not common to have so many host controllers unless you have installed specialized hardware such as multi controller cards. So, I think superspeed refers to internal hubs or ports, whereas the extensible refers to your host controller. Having blue ports simply means that the port routes back to a USB 3 host controller, and sometimes the ports are red as well.

• in college i found out you can have a maximum of 255 usb devices hooked up to a computer at anyone time.

the thing we plugged into 255 usb ports was a usb humping dog :P

• What about USB 3.1 Gen2 (10gb)? Someone have tested 10 ports usb 3.1 gen2 hub?

• ok so please correct me if I'm wrong but what I see is that I have 1 usb 3.0 controller and two usb 3.0 ports going to that controller then the othe usb port I have is 2.0 does that look correct?

I currently have 4 externals hooked up 2 8tb wd my books to a 4 port usb 3.0 hub to port 2 3.0
1 wd my book 4tb and 1 wd my book 6tb to another 4 port usb 3.0 hub to port 3
I currently have my mouse hooked up to port 1 but if all ports are 3.0 I want to do another hub in port 1. all ports are blue.
at what point will my controller start to bottleneck?

I'm on a dell inspiron 15 7000 series with a i76400hq and a NVidia geforse gtx 760 (I think may be off on video card cant figure out how to utilize it to much yet) 1tb hard drive and 8gb ram I believe with a easy upgrade slot or two for more ram.

I'm currently trying to figure out how to scale right now. I'm back to work soon and I want to keep pushing this laptop until it explodes :) I spent almost as much on insurance and replacement plans on this as I did on the laptop and I really regret not getting a desktop instead. If I push it to far and it craps out that's cool I will get a gift card for the price if not its whatever to. I'm a honest guy so I wont do anything to intentionally break it but I will get everything I can out of it haha. so my plan is to scale as far as I can with externals until I hit my bottleneck then burst mine well cpu mining vrm at the same time. I'm not going to get anymore of the eight tb drives because the read times on the 4tb and 6tb are faster (correct me if I'm wrong lol)

so with all that info what would you guys do to add on to what I have if you had this same set up?

• @explosive I'm going to move this to its own thread

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