SD Card not mounting on my Mac

SD Card not mounting on my Mac

If you have a Mac with an SD card slot or even if you use an external USB SD card reader, you would normally expect your card to mount right on your Mac’s desktop or even launch an associated program, such as iPhoto or Aperture.

  1. When an SD Card fails there are a few different behaviours that you can expect:
  2. The device does not respond and is not mounted on or accessible to your computer at all
  3. The device may mount but show random garbage characters when you try to access it
  4. The card may appear to mount but make your system grind to a halt until it is physically removed

But by far the most common failure type that we are presented with by our clients is a message box which appears when the card is plugged in and says…

The disk you inserted was not readable by the computer.

Beneath this you get the option to Initialize… Ignore or Eject.

This can be a little daunting to the uninitiated and can even be caused by a number of different things, lets look at what our Mac is trying to do:

Why won’t my Mac mount my SD Card?

Whether an SD card, USB memory stick, Compact Flash card or an external hard drive, every external storage device needs to be readable to you Mac so that it can treat it as a storage volume and mount it on your system. When this can’t happen there can be a number of reasons the first thing to consider is whether the SD ‘should’ work with your Mac – normally it would work out of the box, but if used with an operating system that formats the card in a way unfamiliar to your Mac, it may be that there is nothing wrong with the device at all.

After ruling that out we have two main problems remaining:

Corruption: perhaps the card was not safely removed from the device that it was last inserted to, or this device had a bug or a glitch that caused the file system to be left in a corrupt state – in either of these scenarios, your data should be fully retrievable.

SD Card Failure: Many popular SD Cards can fail in a manner that leaves them still recognised by a computer. These devices often show up with a different capacity to the one printed on the label (often 1GB, 16MB or 2TB!), but can show up as normal. When this happens the entire data area of the card is innaccessible to your Mac and any attempts to access or write to the card will fail (including attempts to initialise or format the card). In this scenario, the only available option is professional data recovery from Flash Data Recovery.

What should I do?

Generally, an unmountable storage device indicates that the device itself has a serious issue. It could be as simple as a damaged partition table or file system but it could also be indicative of a failed device. It is very difficult to tell what the underlying cause of the fault is without some in-depth diagnostics and tests.


If you have very precious or irreplaceable data stored on your SD card or memory device, it is critical that you do not attempt to initialise it. If the device has actually failed you will be unable to complete this process anyway, if it is just a partitioning or file system issue though, the process should finish without any dramas, however, your data WILL be gone. Contact Flash Data Recovery for more help or guidance if your mac is not allowing you to access your SD card.

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