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Resolved Failed Fusion drive - how do I boot from external SSD? (iMac 2013)

J

JVNeumann

macrumors member
Original poster
Mar 23, 2017
85
26
UPDATE:
So I now have the SSD (Crucial MX300), but I can't get it to boot from / install OSX onto that drive. I open Recovery Mode, but only my standard HDD shows up as an option. The SSD appears in Disk Utility, so it's definitely 'there', it's just not registering as an option to install OSX or boot from. The drive is already formatted as Mac OS Extended.

Any ideas how to get it running?

ORIGINAL:
As per the title, my iMac drive died recently, but considering the machine is otherwise fine I'm hoping to at least keep it running until they refresh the iMac line-up. So I'm thinking of just booting directly from an external SSD, and was looking for opinions on a good medium sized SSD (500gb or so) that'll work with a 2013 (Thunderbolt 2, I think...?) machine.

Perhaps more importantly, can anyone talk me through the actual pipeline for setting up OSX this way when I don't have an install disk, nor do I even have a bootable drive? I assume I do the online recovery mode boot-up, but I'm a bit hazy about what happens after that: will I just select my new external drive in Disk Utility and then some option will appear to re-download OSX for it?
 
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For consumer-grade SSDs, Thunderbolt doesn't have that many advantages over USB3. Here's a 500GB USB3 SSD that will support booting your Mac.

When you get the SSD, connect it to your mac. Use Recovery Mode to launch disk utility, and format your new drive in OSX Extended. Then pick the drive as your main install drive.

You may need to hold option on boot up and select your USB SSD every time you power on your machine from all-the-way off.
 
I would disagree with you spyguy.

I use a TB Silicon Power SSD as an external backup via SuperDuper. Using Smart Copy to do a weekly SmartCopy backup, speed is 344MB/ps. Using an SSD OCZ in a USB3 case doing an identical backup, speed is very limited to about 56MB/ps. Time elapsed is 3 minutes 20 seconds to eleven minutes forty two seconds respectively.

You will boot from your external drive each and every time if you select it in System Preferences > Startup Disk as the boot drive.
 
OP:
You didn't really tell us very much about WHAT "died" in your iMac.
Could you cue us in a bit about which iMac you have, what went wrong, and which drives (if any) are still functional?

Having said that, yes, you can boot and run the iMac from an external boot drive.
The process is so trivial you'll wonder why you even bothered to ask the question here.
Just set it up and run it as you would an internal drive (see additional comments below).

The Macintosh doesn't particularly care from which drive it's booted. It can be internal, external, USB drive SD card, DVD, etc.

You don't need a Thunderbolt drive.
USB3 will be fine.
It won't be as fast as an internal fusion drive or SSD, but it will still run 3-4x as fast as an internally-mounted platter-based hard drive (HDD).

With a USB3 SSD (in an enclosure that supports UASP), you will see read speeds of 430+mbps and writes from 275-340mbps (depending on the drive and size). More than "fast enough" for day-to-day usage.

Don't let ANYONE on this forum browbeat you away from USB3 because "USB3 external drives don't support TRIM".
TRIM is a non-issue, a boogeyman insofar as booting and running from an external USB3 drive is concerned.

I've been booting and running a late-2012 Mini for over FOUR YEARS now from an SSD mounted in a USB3/SATA dock (with UASP support). The setup benchmarks as fast today as when I first booted it.
TRIM has NEVER been an issue.

You don't have to spend a lot for a high-capacity SSD.
Since you just really have to "extend the life" of the current iMac, I'd suggest either a 240gb or 480gb SSD.

Setup:
Just install the OS as you would on an internal drive, i.e...
...Put the OS, apps, and your accounts* onto it.
* -- keep large libraries of music, movies and pics elsewhere (perhaps a second HDD), and "reference" them.
Do it this way, and you'll keep the SSD "lean and clean" for optimum performance (as I've done).

I would suggest either a Crucial or Sandisk SSD.
Lots of folks recommend Samsung, but whenever I see a message posted from someone having a problem with an SSD, it's one of those!
 
nambuccaheadsau said:
I would disagree with you spyguy.

I use a TB Silicon Power SSD as an external backup via SuperDuper. Using Smart Copy to do a weekly SmartCopy backup, speed is 344MB/ps. Using an SSD OCZ in a USB3 case doing an identical backup, speed is very limited to about 56MB/ps. Time elapsed is 3 minutes 20 seconds to eleven minutes forty two seconds respectively.

You will boot from your external drive each and every time if you select it in System Preferences > Startup Disk as the boot drive.
Click to expand...

It's your "USB3" enclosure. The speeds you're stating seem to indicate USB2 transfer speeds. I can personally verify that I'm getting better speeds on a USB3 SPINNING hard drive, and that other people are getting much better speeds on the SSD I linked.
 
if your fusion drive "died" then it was probably just the traditional hard drive component. you should be able to reformat it and "break" the fusion drive and use your internal SSD as a boot volume. then you can get a normal HD or SSD in external format and use that for file storage rather than booting off of it.
 
I agree with kwik above.

If the SSD portion of the fusion drive is "recoverable", keep using it.
Let the internal HDD portion (if dead) remain "dead". Just "leave it be".

Set up the internal SSD to be the boot volume, and plug in an external HDD (or SSD).

This will really only work IF the iMac in question has a 128gb SSD portion.
IF it's only a 24gb SSD (such as on the "1tb fusion model" iMac), it won't be enough room for the OS, apps, and basic accounts.
 
nambuccaheadsau said:
Using an SSD OCZ in a USB3 case doing an identical backup, speed is very limited to about 56MB/ps.
Click to expand...

You are either on a USB2 connection or something else is seriously wrong. I have a USB3 UASP enclosure with a Samsung SSD and can get close to 400MBps.

OP> Just grab a USB3 UASP enclosure and pop a SSD in there (Samsung EVO or Crucial MX300 are popular) and use Internet recovery (command-option-r boot) to format the drive to Mac OS Extended (Journaled) then install the OS to the external drive.
 
Thanks guys. Have been a little quiet for a few days (busy at work), but I've been reading through this. So if I go with USB3 enclosure instead of TB, would something like this plus this be suitable?

Or do people have better enclosure ideas? I'm happy to pay more for better, but this one had good reviews for the size / function.
 
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Okay, so this finally arrived in the mail today... however I'm having trouble setting it up.

I start by booting in recovery mode, but when I choose "Install OSX" it only shows my existing hard-drive as an available option. However, I can see the SSD when I go to disk utility. Am I meant to format it in there first? It does say it's already formatted as Mac OS Extended, so I'm not really sure what to do from there.
 
JVNeumann said:
However, I can see the SSD when I go to disk utility. Am I meant to format it in there first? It does say it's already formatted as Mac OS Extended, so I'm not really sure what to do from there.
Click to expand...
Yes, you need to format the new drive to Mac OS Extended (Journaled) in Disk Utility first.
 
Weaselboy said:
A new SSD like that out of the box is not likely already formatted for a Mac. Just go ahead and do it again anyway.
Click to expand...

You're quite right. Turns out it was just indicating what I could format it to; the layout of that tab is very counter-intuitive. Thanks for your help.
 
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I don't know if you are aware that Apple had an extended warranty on certain fusion drives. Mine failed and even though it was not covered by the program, Apple replaced it for free. Suggest you call apple support and let them walk you through troubleshooting. They may replace it for you.

JVNeumann said:
UPDATE:
So I now have the SSD (Crucial MX300), but I can't get it to boot from / install OSX onto that drive. I open Recovery Mode, but only my standard HDD shows up as an option. The SSD appears in Disk Utility, so it's definitely 'there', it's just not registering as an option to install OSX or boot from. The drive is already formatted as Mac OS Extended.

Any ideas how to get it running?

ORIGINAL:
As per the title, my iMac drive died recently, but considering the machine is otherwise fine I'm hoping to at least keep it running until they refresh the iMac line-up. So I'm thinking of just booting directly from an external SSD, and was looking for opinions on a good medium sized SSD (500gb or so) that'll work with a 2013 (Thunderbolt 2, I think...?) machine.

Perhaps more importantly, can anyone talk me through the actual pipeline for setting up OSX this way when I don't have an install disk, nor do I even have a bootable drive? I assume I do the online recovery mode boot-up, but I'm a bit hazy about what happens after that: will I just select my new external drive in Disk Utility and then some option will appear to re-download OSX for it?
Click to expand...
 
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OFLawyer said:
I don't know if you are aware that Apple had an extended warranty on certain fusion drives. Mine failed and even though it was not covered by the program, Apple replaced it for free. Suggest you call apple support and let them walk you through troubleshooting. They may replace it for you.
Click to expand...

Thanks for the heads up, but this machine is going on 3.5 years - is that still likely to apply to me?
 
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