bootable USB 3 external drive for new iMac

All USB 3 external drive I have used or seen use a special connector at the drive. Not the standard USB connector used on any USB 2 drives I've ever worked with. I don't use portable drives that are powered off the USB port.

My USB3 drives are all bus powered. But they have a special connector, probably the same as your drives. It is split into two unequal parts by a plastic triangle. A standard mini USB cable like many USB2 drives use will not fit. But I have been told that a micro USB cable, as used for some phones, will plug in to one side of the split USB3 jack and let you run the drive in USB2 mode. Can't verify that myself. And of course you can use a USB2 hub between the USB3 drive and the Mac. That's what I used.

Able to boot up from USB on late mb air 2011.

Same 3.0 jump drive is NOT able to boot on my new late 2013 ssd retina mbp.

Same drive.

Same image on it via superduper.

Works on 2011 air but not on new mbp late 2013.

Not sure of the reason but what I have found.

Received late Feb. 2014, 27" iMac 3.5 GHz Quad-core Intel Core i7 with an internal 512 GB SSD running Mavericks 10.9.2 on which I created 3 partitions.

Bought from Apple Store, LaCie 256 GB Rugged USB 3.0 Thunderbolt Series SSD Hard Drive on which I have 2 partitions using CCC 3.5.4 to clone Mavericks to each partition.

There is no problem booting from this external drive using USB 3 or Thunderbolt although the drive is connected to the USB 3 port on the iMac rather than the Thunderbolt port as the USB connection is surprisingly, a little faster than the Thunderbolt connection especially on reads. Writes average 300 MB/s and Reads average 425 MB/s.

This is not really surprising to me.

The 2011 Macbook Air has USB2 ports, so the drive operates in USB2 mode, which is fine for booting on any Intel Mac.

The 2013 MBP has USB3 ports, so the drive operates in USB3 mode. Obviously your MBP must have the same boot ROM limitations as my 2012 MBP. I am quite certain that if you connect that drive via a USB2 hub, so that it operates in USB2 mode, it will boot.

I have not had any response yet from Apple on my bug report. They will have to make a business decision on whether it is worth issuing new boot ROM images for the Macs that have USB3 ports but can't boot from a USB3 drive in USB3 mode. Since some recent Macs can boot from USB3, they have obviously found a solution. But merging that solution into many different boot ROMs, some of which may be tight on space, would require a fair amount of work especially to verify that the fix does not break something else.

They have three choices for how to implement USB3 booting.

- The easiest fix is to have the boot ROM force any USB3 drive to operate in the slower USB2 mode.

- A better fix is to boot in USB2 mode, but once OSX has loaded (at the login prompt) switch to USB3 mode.

- The best fix, but obviously the most work, is to boot in full USB3 mode from the start.

Jimity, can you determine which of these seems to apply to your new iMac?

As stated in my previous post, my new iMac (27-inch, Late 2013) boots fine with the LaCie 256 GB Rugged USB 3.0/Thunderbolt Series SSD Hard Drive connected either by Thunderbolt or USB 3.

Today, I tried a USB 2 extension cable between the iMac and the LaCie USB 3 drive and found Write speeds averaged 37 MB/s and Read speeds averaged 38 MB/s. As mentioned in my previous post, the LaCie drive with USB 3 cable connected had Write speeds of 300 MB/s and Read speeds of 425 MB/s. Much faster with USB 3.

I then checked what USB speed mode the LaCie drive started up with by first starting up with the USB extension cable connected and then with it removed. It took 33 seconds from startup to login screen with the USB 2 extension cable connected and just 20 seconds with only the USB 3 cable connected. If the external USB 3 drive was starting up in USB 2 mode, both ways should have had the same startup time but this was not the case.

So, to answer AI Q's question from his previous post, the external LaCie SSD drive appears to boot in full USB 3 mode.

A surprise came when trying to start up from a Lexar 16GB USB 3 flash drive with Mountain Lion 10.8.5 on it. My computer is the newest iMac presently available and came pre-loaded with Mavericks, so I assumed it would not start up with Mountain Lion but it did.

I had heard that you could not start up with a previous version of the operating system from that which came with your computer but this proves otherwise. Is this a change now that system software is downloaded and no longer supplied with the computer on DVD?

Can a computer which came with Mavericks installed run with Mountain Lion AND be software legal?

Booting in full USB3 mode is great news. I just hope that Apple puts that code into an updated boot ROM for my computer and the many others that are forced to use USB2 now.

I don't see any licensing problem with using Mountain Lion on your computer. The fact that it works suggests that Apple did build support for your hardware into that late release of Mountain Lion.

An interesting sidelight: If you have Parallels Desktop 9, you can boot not only Windows and Linux along with Mavericks, you can also create a virtual machine to run earlier Mac OSX releases. I might go back and create a VM that can run the emulated PowerPC code that recent OSX releases do not support. In particular, I would gain access to old AppleWorks files that Pages unfortunately does not handle correctly.

We know that USB3 drives always work when connected in USB2 mode (either to a native USB2 port or via a USB2 hub). The very latest Macs seem to be able to boot in USB3 mode with high quality USB3 drives like your Seagate. But as soon as anything is a little off (generic USB3 cases, for example, or encrypting the drive with Disk Utility) it may not work.

I've recently had a final answer from Apple. They do not intend to fix the boot ROMs of older Macs such as my 2012 MBP that have USB3 ports but cannot boot in USB3 mode.

I hope that they do at least create a KB article telling people to use a USB2 hub or cable to get around that limitation.

Can a computer which came with Mavericks installed run with Mountain Lion AND be software legal?

Licensing wise there is no problem - I am running Snow Leopard, ML, and Mavericks. However, Macs have never been able to boot from an earlier OS version than what they came with.

If yours is one that was manufactured right around the time Mav came out, the build may still support ML (as it was originally meant to), but Mav was then loaded. That machine might be able to be booted from ML. You'd have to install ML onto an external drive, boot from it, partition your hard drive (that would include erasing it), and install ML in one partition. Or, you could simply run ML from the external while booted from it.

Another option, if you have Parallels Desktop, is to run an earlier Mac OS release in a virtual machine under Mavericks. That can be particularly helpful if there are only a few old programs you want to run.

I have a mid-2012 MacBook Pro Retina 15" with two USB 3.0 ports, Mavericks up to date. I am using a WD MyBook Essentials USB 3.0 1.5 TB external drive. It has no Thunderbolt or Firewire port.

I can make a clone on the external drive and boot from it using either USB 3.0 or attaching it to a 2.0 hub. It boots, but the problem is that it runs so slow as to be essentially unusable. And it hangs all the time. I don't know what the read and write speeds are when booted into the external drive, but the drive seems pretty fast when making the clone on USB 3.0 or backing up to the Time Machine (which is also on the drive). I even made a new partition and installed, without problems and pretty fast, a new Mavericks on the second partition. Again, it boots fine but runs like cold molasses.

I'm wonder whether the problem is with the drive or with the USB 2.0/3.0 interface of the rMBP. The rMBP runs very fast on its own internal SSD, so i don't think it's an OS or configuration issue.

Should I just get an external SSD? $$$ :-(

Any thoughts would be appreciated.

Great to hear that your Retina MBP will boot from USB3, unlike my non-Retina MBP, same vintage, which boots only when I connect through a USB2 hub.

I have since repartitioned an older 750 GB USB3 drive with a 512 GB partition for a Super Duper clone of my Mavericks system and the rest for a fresh Mavericks install with Disk Warrior and a few other utilities added. I used Disk Warrior to optimize the directory structure of both of those (running from my internal SSD, with the external drive connected as USB3). That speeded up booting and normal running from either partition (USB2 connection of course) noticeably.

My cleanup process (every few months) is to Smart Update the clone partition (USB3), then boot from my small Mavericks+Disk Warrior partition (boots pretty fast despite USB2) and run Disk Warrior on my internal drive. If there were no major errors found (always the case so far) I then boot back to the internal drive and run Disk Warrior on the clone so that it will be faster if I ever need it. Cleaning up the directory structure has less performance impact on an SSD, but it ought to catch any directory corruption before it spreads.

I used to take advantage of the ability of Super Duper to share the same partition for clone and Time Machine. It should make better use of drive space, but there is one big flaw. A long term Time Machine backup accumulates huge numbers of links. The latest version of Disk Warrior can process them, but it takes many hours, and I once had it quit saying it had run out of memory (I think that drive was fairly badly corrupted). With Time Machine and clone on separate drives, I can clean up the directory structure of the clone in a reasonable time, and I am protected if either external drive dies.

I should probably run Disk Warrior overnight on my Time Machine drive (with Time Machine off, and Sleep set to never, of course), but I have not tried it since I got my new drive for Time Machine.

Good news. All of my Seagate usb3 drives boot with usb3 Yosemite. Thanks Apple for fixing the problem. No more slow usb2.

Bob

Al Q wrote:

Apparently some recent Macs (2013 vintage) will boot from USB3, though it has been reported that they do not support encrypted USB3 boot drives. But I would not be at all surprised to discover that the Genius Bar was using USB2 cables, since that avoids all the USB3 issues.

I was at the Genius Bar a couple of days ago and compared my bootable USB 3 SSD drive+Enclosure (a Startech model) with their LaCie bootable USB 3 model because I suspected that there was a similar issue on my new (2014 15" rMBP) machine.

It turned out that the startup was flaky due to the drive as we were able to try several combinations of machines, drives to prove the problem went with the enclosure+drive and not the machine by trial and error. So I'm trying a Yosemite clean installed SSD in yet another enclosure, I've been through three Startech enclosures and found that there is some kind problem with certain USB bridge chipset in these enclosure that apparently have interface issues with Apple USB connections (it seems to correlate to the AS Media 1051/1053 chipset. The next one I am trying is the 1053e chipset which according to OWC is supposed to work. I will report back on my tests with that when I get it. Apple states unequivocally that an external drive should startup in USB3. I did not ask whether that's also true of USB via a Thunderbolt interface, but will try that as well.