completely OT

Christopher Chavez chrischavez at
Sun Apr 21 05:18:48 UTC 2019

On 4/14/2019 3:49 AM, James Linder wrote:
> Hi
> I have a mid 2011 iMac. I setup a SSD on usb3 over thunderbolt.
> All good EXCEPT that it wont boot. Will boot on the usb2 ports but they are slower than usb3.
> I'm looking for a pointer or advice on how to boot on diskA say the internal disk, but run (root on) diskB
> I can't find a thunderbolt 1 disk or adapter
> Can anybody point me at where I could ask these sort of questions
> sorry for last-resort posting here
> Thanks
> James

Hi James,

I want to try clarifying the hardware issues here, so that maybe you
won't have to resort to straddling the internal drive and an external
drive. From what I've gathered, I would be optimistic that there is at
least one better arrangement than booting from USB 2 with your iMac.

One option is FireWire 800, which is about twice as fast as USB 2 (and
FireWire 400). If you find a FireWire 800 SSD, or an "enclosure" that
you put your own SSD in, your iMac will almost certainly support booting
from it. However, this option has become less worthwhile or future-proof
due to FireWire being absent from recent Macs (which would require a
Thunderbolt to FireWire adapter) and for being slow compared to
Thunderbolt or USB 3.

The other potential option is…Thunderbolt, but using a drive that
connects directly to Thunderbolt, rather than through a USB 3 hub/dock.
It's not clear to me whether your iMac can support booting from any
given Thunderbolt drive or only certain ones (e.g. depending on whether
the drive internally uses the newer PCIe/NVMe interface instead of the
older SATA/AHCI interface; or what specific firmware and macOS versions
your iMac is running), or none at all. I think that some Mac-oriented
vendors like Sonnet or OWC might be more knowledgeable on questions like
whether your model iMac will support booting from a particular
Thunderbolt drive of theirs and under what conditions.

Also, there *is* a way to connect your Thunderbolt 1 iMac to Thunderbolt
3 devices: Apple's bidirectional Thunderbolt 2 to 3 adapter, MMEL2AM/A.
Some caveats include that the Thunderbolt 3 device must have a separate
power source, the Mac must be running 10.12 Sierra or later, and of
course it will only run up to Thunderbolt 1 speeds on your iMac.

Hope this helps

Christopher A. Chavez

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