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  1. #1


    Member Since
    Jul 25, 2011
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    15
    My new Mac won't recognise my external drive
    I have recently bought a Mac and am switching from a PC.

    I had a 2Tb external drive that I was using to back up the PC and having moved all my files across to the Mac, I transferred the external drive at the weekend.

    It seemed so easy, it was a plug and play, the Mac recognised the new drive as soon as I plugged it in to one of the USB ports and proceeded to set it up as the 'Time Machine' drive after warning me that it would format it and did I really want to erase all the data on it.

    Too good to be true? It seems so, because I turned the Mac off on Sunday evening and on Monday evening when I rebooted the Mac failed to recognise the 2 Tb drive - it just didn't exist until I unplugged the USB cable and re-plugged it in again. Bingo the Mac recognises the drive and shows my back ups from the previous day.

    So..... Yesterday evening I re-formatted the drive and set it up as the back up again. This morning I booted the Mac up and same result - nada - nothing!

    I shut the Mac down and - re-booted, this time it recognised the external drive without me having to plug and unplug it. I would add that I didn't wiggle any of the wires or touch anything apart from the keyboard and mouse - oh... and the start button on the back.

    Is there anyone out there who can tell me what is going on and more importantly what can I do to fix it? I thought it was only PCs that had a mind of their own!

  2. #2

    MacInWin's Avatar
    Member Since
    Jul 07, 2008
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    2015 rMBP, 2008 iMac, iPhone 7, iPad mini, 13" MBP, AppleTV and two MacMinis
    It sounds like the drive is going into a power-saving mode that does not wake up when the USB port is reactivated. I have had the same problem with USB external enclosures before. I have now switched to all Firewire external drives and the problem has disappeared. I never found a fix. (BTW, I had the same problems with those drives in Windows as well, so it wasn't OS-specific, more hardware interface related.)

  3. #3


    Member Since
    Jul 25, 2011
    Posts
    15
    Thanks for the reply Jake but I don't think that is the answer.

    When I boot the Mac it kicks the external drive into action because the light comes on an the thing starts to spin. And I never had any problems with it running on the PC - it is only a few months old.

    What is Firewire is that a faster port and can I connect a device that came with a USB cable via a Firewire connection provided I use some sort of adaptor?

    Rgds Ian

  4. #4

    MightyGem's Avatar
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    Nov 29, 2010
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    Specs:
    PPC Mini, 10.4.11. Intel Mini, 10.6.8. MacBook Pro, 10.10.5. iPhone 3GS.
    I don't think that there are firewire to usb adaptors as firewire transmits data in a different way to USB. It sounds like you have an iMac which has a Firewire 800 socket but you'll need one on the external drive to use it.

    Have you tried a different USB port/cable?

  5. #5

    MacInWin's Avatar
    Member Since
    Jul 07, 2008
    Location
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    6,714
    Specs:
    2015 rMBP, 2008 iMac, iPhone 7, iPad mini, 13" MBP, AppleTV and two MacMinis
    When you BOOT the iMac, it does restart the USB ports and that signals to the drive to wake up from it's sleep mode. But when you just let the iMac go to its sleep mode, when you WAKE IT UP it doesn't send the USB port any signal, it just expects the device to be there just like when it went to sleep. So the external drive doesn't get a wake up signal and it stays in sleep mode. At least that is what I was able to determine. My drives were from Seagate. They had a software patch that was supposed to fix that problem, but the patch didn't work. Drives are relatively cheap these days, so I went out and got a new drive with Firewire interface.

    I don't think there are easy ways to bridge USB to Firewire, as MightyGem said, but there may be something. It's worth looking for, I guess, but I suspect that the wake up signal may not be there either, as the interface is entirely different.

  6. #6


    Member Since
    Jul 25, 2011
    Posts
    15
    Yesterday evening, I tried shutting down and rebooting the iMac and as I said although the light started to flicker on the external drive (showing it was working) the Mac didn't recognise it if I went into 'Finder'

    However, I moved the cable to a different USB port and this morning when I booted up the iMac it recognised the external drive.

    I will see if it continues to recognise it.

    Rgds Ian

  7. #7

    chscag's Avatar
    Member Since
    Jan 23, 2008
    Location
    Keller, Texas
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    Specs:
    Late 2013 27" iMac, iPad 3, iPhone 6s+, iPhone 6+, 3 iPods, Sierra
    Is your iMac new? (You didn't tell us anything about your Mac) Generally, an iMac provides more than enough power through its USB ports to spin up most external hard drives. It sounds like perhaps one of your ports is not giving the drive enough power or they're may be something wrong with the drive itself. Keep us posted.

  8. #8


    Member Since
    Jul 25, 2011
    Posts
    15
    Yep! Brand new 21.5".

    The drive is a 2Tb Western Digital item so its not a cheap item and it never gave any problems when attached to the PC.

    I tend to shut the IMac down at night but it is left on standby in sleep mode during the day. Hopefully tomorrow it will carry on doing the right thing.

    It's weird because on the port I originally had it plugged into, the iMac would immediately recognise the drive when it was plugged in. But, when I booted the IMac it would kick the WD drive into life but not recognise it. And if I unplugged and re-plugged the drive, then the iMac would 'see' it again.

    We'll see what happens tomorrow.

    Rgds Ian

  9. #9

    chscag's Avatar
    Member Since
    Jan 23, 2008
    Location
    Keller, Texas
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    Specs:
    Late 2013 27" iMac, iPad 3, iPhone 6s+, iPhone 6+, 3 iPods, Sierra
    It's beginning to sound like that drive may have flakey firmware. Let us know how it goes.

  10. #10


    Member Since
    Jul 25, 2011
    Posts
    15
    I wouldn't have thought it was the drive that had flakey firmware because that has always worked before. To me, it seems that one of my USB ports may not be working properly.

    Anyway, for the time being, I hope it's problem solved and thanks.

    I do have another problem - I'm just about to post it.

    Rgds Ian

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