Wednesday, April 3, 2013

OSX Mountain Lion 10.8 UAS UASP USB Attach SCSI drivers

My blog was one of the first to write about UAS/UASP (USB Attached SCSI) on the Mac OSX platform last summer. I've been writing about it for some time.

I've been getting a lot of Google search query hits on my blog for "Mountain Lion UAS drivers", "OSX USB Attach SCSI", and "OSX UASP drivers."

Well, here is the answer for all those daily search queries in this blog post. If you came here from a search engine, this blog will help you find your answer.

What is UASP? In short.

  • Enables storage products to operate much faster by utilizing the faster bandwidth now available with the new Super Speed (USB 3.0) standard
  • Reduces the protocol overhead of Bulk-Only-Transport (BOT)
  • Supports SATA native command queuing (NCQ)
  • Multiple commands are processed in parallel

There is no "drivers" for UAS/UASP. If you have Mountain Lion, the "drivers" will be system kexts located at: /System/Library/Extensions

There are two USB kexts that OSX uses for mass storage:


The first one for standard, traditional Mass Storage BOT (Bulk only transport) and the second for UASP. Even old Macs without USB 3.0 UASP ports will have the IOUSBAttachedSCSI.kext installed. It doesn't mean your Mac has UASP hardware.

To find out if your Mac supports UASP, here is a simple test.

Plug in a USB device. Go to  "About This Mac" > More Info > System Report  and scroll down to "Extensions" under Software.

If you have a BOT (aka regular USB drive) device, the IOUSBMassStorageClass will load up. A simple test is to plug in an older USB 2.0 stick/drive. See screenshot below.

Now, quit the "About Mac / System Information applet" and plug in your USB 3.0/UASP drive. Reload the About This Mac and repeat the previous step.

If  the following "IOUSBAttachSCSI" shows up, your Mac takes advantage of the faster SCSI USB like protocols, UAS.

I've notice that if you plug your device into a USB hub, it does not load up the UASP kext.  So take note. Even with some USB 3.0 hubs, the device will drop down to BOT Mass storage. This will be interesting to take note in the future.

Simple. Now, you don't have to Google around anymore for OSX "UASP" drivers. It is all there in Mountain Lion. The kext will load on-demand as your plug in your UAS/UASP USB 3.0 Super-speed devices.

Now, if you want to see UASP in action, here is a review of a UASP device in OSX: the Blac X 5G and a youtube video of it's speed below.

1 comment:

  1. I am using AKiTiO Thunder Dock, a hub you can link to your mac through only thunderbolt cable.

    This hub provides multiple host ports, including eSATA, USB3.0, Firewire800, and thunderbolt as well.

    But, I just found out despite the hub linked to my mbp 15" 2011 early,

    my external drive is still working through BOT(IOUSBMassiveStorageClassic.kext) instead of UASP (IOUSBAttachedSCSI.kext).

    Even when UASP driver was loaded manually, the transfer rate is still as low as USB2.0.

    is there any solution?

    or it just doesn't work on my mbp 15" 2011 early?