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I noticed that I could remount my USB hard drive through terminal after I eject it by typing diskutil list to find the drive and diskutil mountDisk /dev/disk"X"...

So I tried to do the same with my SD card and my USB flash drive but...after I eject them, I cannot find them anymore through diskutil list.

I suspect this is because they are not "drive" until the system determines them as drives...which happens automatically when you plug them in - and the system remove those drives from the USB interfaces/SD card interfaces after I eject them.

So, the question is, how do I manually determine these USB interfaces/SD interfaces as "drives" so I can remount them. Thanks.

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There's a difference between unmounting and ejecting. I'm not familiar with the CLI of diskutil, so I'll explain it using Disk Utility.app

When you have a mounted SD card you can unmount it by clicking the Unmount button in the Toolbar: enter image description here
The SD card stays in the list, but it is faded out. Then if you want to remount it again, just select the SD card and click Mount:
enter image description here

  • Right, this is helpful. But how to I digitally re-insect the USB flash drive or SD card after I eject them? – aeroxy Mar 8 '14 at 18:46
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so I figured this out. First of, SD card and USB flash drive use different kernel in OS X, so the solution is not universal. Fist of, if you use USB flash drive:

In your terminal type

sudo kextunload /System/Library/Extensions/IOUSBMassStorageClass.kext

Type your password (use an admin account), then

sudo kextload /System/Library/Extensions/IOUSBMassStorageClass.kext

What this does is that it unload and reload the USB storage kernel extension system wise, so it is an equivalent of unplug and replug your USB storage device after the ejection.

Similarly, we can do that with SD card reader too! Type:

sudo kextunload -b com.apple.driver.AppleSDXC
sudo kextload -b com.apple.driver.AppleSDXC

Tada!

Be careful tho, once you unload the kernel and forget to reload the kernel, you will not be able to read the device at all even if you physically unplug and plugin the device.

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