Question on USB ports on new Mac Mini

Discussion in 'Mac mini' started by grkmec, Aug 24, 2011.

  1. grkmec macrumors newbie

    Joined:
    Aug 15, 2011
    #1
    Are the 4 USB ports on the new Mac Mini independent? In other words, if I connect 4 external DVD drives to rip movies simulateously, will I saturate the USB channels to the point that ripping multiple dvds doesnt make sense?
     
  2. Gav2k macrumors G3

    Gav2k

    Joined:
    Jul 24, 2009
    #2
    Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_3_3 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8J2 Safari/6533.18.5)

    I just tested with two hdd's seems there 2x2 so if you put a hdd in 1+2 and transfer a file its slow as it picks files up pauses and transfers. If you use 1+3 then it flies along.

    Hope that helps
     
  3. indg, Aug 24, 2011
    Last edited: Aug 24, 2011

    indg macrumors 6502

    Joined:
    Feb 7, 2007
    #3
    theory below is invalid, but i'll leave it up for posterity:

    here's my theory (meaning this is just a guess)... all the usb ports connect over a single 480Mbits/s pci bus. so connecting 4 drives would split that 480 to 120Mbits/s each or about 15MBytes/s. with overhead, probably drops down to 8-10MB/s. so unless each drive is reading the dvd at over 8MB/s (64Mbits/s), 4 drives should be ok in theory. now whether the cpu can keep up with 4 separate dvd rip/transcodes is another matter. if you're just ripping the vobs to hdd, then it might be ok. if you're transcoding (e.g. handbrake), then even the quad i7 probably wouldn't be able to keep up with 4 separate transcodes to saturate the usb. again this is all just a guess on my part.
     
  4. grkmec thread starter macrumors newbie

    Joined:
    Aug 15, 2011
    #4
    The way I understood it was than USB port 1&2 share a channel, and ports 3&4 share another channel. So, if you put 2 really fast DVD drives onto channels 1&2 vs. say 1&3, it will be much slower.

    The reason I asked the question was last night I hooked up a DVD drive to a USB and ripped 8GB in about 14 minutes. I then added a 2nd DVD drive and tried ripping 2 at once, and it took like 30 minutes. So, I think the DVD saturated the USB. I think I used Port 2 & 3 and I wasn't sure if the slow down was hardware related or Ripit paused the 1st rip to do the 2nd.

    When I go homne tonight, I will try Port 1 and 3 (or 4) to see if speed improves. Hopefully that will work. I will also try adding a 3rd drive via Firewire.

    I am just ripping - no Handbrake - so very little CPU is being used.
     
  5. indg macrumors 6502

    Joined:
    Feb 7, 2007
    #5
    @grkmec, i think you are right about the 2 channels because one of channels is shared with the bluetooth usb controller. so going left to right when looking at the ports, ports 1 and 2 are on one channel, ports 3 and 4 are on a second channel that is shared with the broadcom hub for bluetooth.

    connect your drives and look in the system information app under usb to see how the hubs are split.
     
  6. indg macrumors 6502

    Joined:
    Feb 7, 2007
    #6
    8GB in 14 minutes is like 10MB/s. i would think the 2 usb ports on a single channel would still be able to handle 20MB/s total. that's well under the sustained 34MB/s i usually get when i do transfer to/from a single USB connected hdd. hmm interesting.
     
  7. clystron macrumors newbie

    Joined:
    Aug 11, 2011
    #7
    Where did the data go?

    When you rip from one DVD-drive its a linear write of ~10MB/s for the HDD which is not a problem but when the second DVD-drive comes into play the HDD needs to seek constantly and it might not be able to sustain ~20MB/s doing that.
     
  8. grkmec thread starter macrumors newbie

    Joined:
    Aug 15, 2011
    #8
    I used port 1 and 4 last night, and the speed was about 15 minutes for 2 dvd ripping simultaneously.
     

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