External drives not connecting

Discussion in 'iMac' started by markel253, Aug 23, 2015.

  1. markel253 macrumors regular

    Joined:
    May 17, 2008
    #1
    Can anyone help me with this problem?

    While away for a few weeks, there had been a power failure. Although my iMac and drives are on a UPS, I have realized that the USB hub was not, and I am assuming that is why the drives disconnected from the computer.

    In the past I would reconnect them and sometimes had to do a repair using Disk Utility. However, this time they are not even showing up on the utility to run a repair.

    I disconnected the drives and reconnected them to my macbook air and the drives work fine and do not need repair.

    Any suggestions?


    Mark
     
  2. jterp7 macrumors 6502a

    Joined:
    Oct 26, 2011
    #2
    they're fine. I have 4 portable drives connected through a hub and this is just how it is...yes I realize not very reassuring. Best to have another backup just in case.
     
  3. rigormortis, Aug 23, 2015
    Last edited: Aug 23, 2015

    rigormortis macrumors 68000

    rigormortis

    Joined:
    Jun 11, 2009
    #3
    a lot of people don't realize the power limitations of usb. usb 2 is only designed to put out 5 v @ 500 ma. usb 3 only puts out 5 v @ 800 ma (or more maybe 900 I'm not sure ). your hard drives could not be spinning up, simply because the usb hub is not providing enough power. hold the hard drives to your ear to make sure you can hear the drive spin and the heads move.

    the exception to this usb power limitation is iPhones and iPods and iPads. they get extra usb current. but in order for the iPhone iPod and iPad to get extra current it must ask for it. from what I've seen , and based on experience, i don't think hard drives ask for anything more then 5 v @ 500 ma

    you need to make sure you are using a self powered usb hub and it provides adequate power to all the drives.

    another bad thing about attaching a hard disk to a sata to usb bridge is that it blocks smart monitoring. thats the worst thing. if your hard drive is failing , you are not going to get any early warning messages, it will just suddenly stop working. if you are using mission critical stuff, always have a backup. always buy drives in retail boxes so you get the manufacturers warranty, and if you are using regular drives in generic cases, remove those drives from time to time, connect it to a computer's internal sata controller , and read the smart status. the last part about reading the smart status is kind of a hassle but if you want to make sure you are covered, it is highly recommended.
     
  4. rigormortis, Aug 23, 2015
    Last edited: Aug 23, 2015

    rigormortis macrumors 68000

    rigormortis

    Joined:
    Jun 11, 2009
    #4
    i felt that 4 usb drives using a hub was kind of excessive and i have had problems with using some drives and having them randomly disconnect on me and spin down, and go beep beep beep beep because they weren't getting enough power, so that is why i posted the previous message.

    also i got a good deal ( FREE ) on seagate hybrid hard drives, i use them for my plex server and time machine. they require 5 v @ .7 a on the label. this is clearly out of usb 2 spec. if you are using a lot of drives on a hub you really should add up the amps of the drives and make sure it doesn't exceed your external hubs power supply
     
  5. markel253 thread starter macrumors regular

    Joined:
    May 17, 2008
    #5
    Thanks for the answers, and I do think that the USB hub may indeed be the problem. When I connected the drives directly to the iMac itself, they all worked fine.

    I have ordered another hub and will see what happens if I use 2 new powered hubs (the old was indeed also a powered hub) and if that makes a difference.

    They had been working off the old hub for quite a long time until this happened, but I will see what a new set-up brings.


    Thanks again.


    Mark
     
  6. markel253 thread starter macrumors regular

    Joined:
    May 17, 2008
    #6
    UPDATE:

    Turns out that all I had to do was re-boot the USB hub. Once I did that everything was okay again.


    Mark
     

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