OS X 10.9 (Mavericks) Problems with USB SD card adaptors and a fix

UPDATE - This improves the problem but you get I/O errors when trying to write large amounts of data to the SD card.

One thing that I have noticed with OS X 10.9 is that USB SD card adaptors have stopped working properly. Generally the SD card will mount and then unmount itself. It will get stuck in a cycle of doing this, leaving notification dialog boxes stating that the disk has not ejected properly.

Investigating the issue I noticed that the version of IOUSBMassStorageClass.kext was 3.6.0 that was delivered with 10.9. The version of IOUSBMassStorageClass.kext that is delivered with the 10.8.5 is 3.5.1. The solution that I have found is to revert the IOUSBMassStorageClass.kext extension back to the 10.8.5 version. I find it suspicious that Mavericks has problems with other USB mass storage devices.

To update the IOUSBMassStorageClass.kext

First make a new folder /System/Library/Extensions-Disabled. Move the IOUSBMassStorageClass.kext version 3.6.0 from /System/Library/Extensions to /System/Library/Extensions-Disabled

Copy the IOUSBMassStorageClass.kext version 3.5.1 file to /System/Library/Extensions. Then, open the Terminal app (located in OS X under Applications->Utilities) and type:

cd /System/Library/Extensions

For those unfamiliar with command line, this just changes the directory that Terminal is working on to /System/Library/Extensions. Then type:


sudo chmod -R 755 IOUSBMassStorageClass.kext
sudo chown -R root:wheel IOUSBMassStorageClass.kext
This fixes the kext's permissions.

Then reboot. If everything went well, then hopefully the newly replaced kext will do the job. It  is a good idea to run disk utility and repair the permissions.