Resolved 2017 iMac 27" external SSD as boot drive?

-Ryan-

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Original poster
Jan 28, 2009
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So, a friend has asked me for advice with his 27" iMac. He bought it with a fusion drive, but is looking to go full SSD due to the relatively slow performance. I have explained that the iMac cannot have the drive replaced without some serious surgery on the system and he isn't keen to go that route as it is still in warranty for another 2 years.

I understand it should be possible to boot from a SSD connected via Thunderbolt or USB 3. I've got a few questions about this.

1. Will only specific drives do this or can I buy any enclosure or external drive and it will work?
2. Which is better for this - Thunderbolt or USB 3?
3. What sort of performance improvement would be achieved over the stock 1TB Fusion Drive with a current generation SSD (connected via Thunderbolt or USB 3)?
4. Has anyone done this long term? Any pros or cons?

Thanks in advance!

EDIT: See my later post for steps taken to upgrade to external SSD.
 
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keysofanxiety

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Nov 23, 2011
9,534
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So, a friend has asked me for advice with his 27" iMac. He bought it with a fusion drive, but is looking to go full SSD due to the relatively slow performance. I have explained that the iMac cannot have the drive replaced without some serious surgery on the system and he isn't keen to go that route as it is still in warranty for another 2 years.

I understand it should be possible to boot from a SSD connected via Thunderbolt or USB 3. I've got a few questions about this.

1. Will only specific drives do this or can I buy any enclosure or external drive and it will work?
2. Which is better for this - Thunderbolt or USB 3?
3. What sort of performance improvement would be achieved over the stock 1TB Fusion Drive with a current generation SSD (connected via Thunderbolt or USB 3)?
4. Has anyone done this long term? Any pros or cons?

Thanks in advance!
1. Will only specific drives do this or can I buy any enclosure or external drive and it will work?

Any drive/any enclosure.

2. Which is better for this - Thunderbolt or USB 3?

On paper Thunderbolt should be a little quicker, but TB2 enclosures would be more expensive. Remember it's going to be 6Gb/s SATA on the drive which wouldn't get close to the theoretical max speeds of TB2 anyway. USB 3 will be quick enough and a cheaper/universalised option.

3. What sort of performance improvement would be achieved over the stock 1TB Fusion Drive with a current generation SSD (connected via Thunderbolt or USB 3)?

The main benefits to SSDs over mechanical drives are the seek times rather than read/write speeds. If they're frequently running applications & data from the 1TB HDD rather than the SSD (which was only 24GB or something IIRC) then the system would feel much snappier.

4. Has anyone done this long term? Any pros or cons?

Should be fine, just ensure the boot drive is set for default (hold Alt on startup, press CTRL to change the arrow icon and press Enter to make that one default). You can easily install & run macOS to/from an external drive. Cons would be slightly reduced performance but for real-world usage it's not really noticeable unless you're doing intensive work.
 

Glideslope

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Dec 7, 2007
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A quiet place in NY.
So, a friend has asked me for advice with his 27" iMac. He bought it with a fusion drive, but is looking to go full SSD due to the relatively slow performance. I have explained that the iMac cannot have the drive replaced without some serious surgery on the system and he isn't keen to go that route as it is still in warranty for another 2 years.

I understand it should be possible to boot from a SSD connected via Thunderbolt or USB 3. I've got a few questions about this.

1. Will only specific drives do this or can I buy any enclosure or external drive and it will work?
2. Which is better for this - Thunderbolt or USB 3?
3. What sort of performance improvement would be achieved over the stock 1TB Fusion Drive with a current generation SSD (connected via Thunderbolt or USB 3)?
4. Has anyone done this long term? Any pros or cons?

Thanks in advance!
I run a 512 T3 SSD as a boot disk on my 2017 27". It's Velcroed on the back and connected via USB-C. I run 10.12 on it as well as my internal SSD. I use it as a 'sandbox" so to speak. Use USB-C not USB 3.0. What does your friend need more speed for from the Fusion? What size Fusion is it? :apple:
 

casperes1996

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Jan 26, 2014
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On paper Thunderbolt should be a little quicker, but TB2 enclosures would be more expensive. Remember it's going to be 6Gb/s SATA on the drive which wouldn't get close to the theoretical max speeds of TB2 anyway. USB 3 will be quick enough and a cheaper/universalised option.
Unless it's a PCIe SSD inserted in a TB enclosure. Much, much, much more expensive, but no SATA limitation.

The main benefits to SSDs over mechanical drives are the seek times rather than read/write speeds. If they're frequently running applications & data from the 1TB HDD rather than the SSD (which was only 24GB or something IIRC) then the system would feel much snappier.
Depends on the drive and what you use it for. SSDs can still have much higher sequential read and write speeds and if you do a lot of sequential reads and writes that could matter too. – And the 24GB thing is also something that should be marked with an *, as it depends on the capacity of the Fusion Drive as well as the model of iMac. The fact that this is 2016 does make it likely it's 24 gigs, but it could be 128 too.

Should be fine, just ensure the boot drive is set for default (hold Alt on startup, press CTRL to change the arrow icon and press Enter to make that one default). You can easily install & run macOS to/from an external drive. Cons would be slightly reduced performance but for real-world usage it's not really noticeable unless you're doing intensive work.
Alternate method is changing Startup Disk in System Preferences.
 
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Fishrrman

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Feb 20, 2009
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He should get a Samsung t5 drive, re-initialize it for the Mac (HFS+ with journaling enabled), and then install a copy of the OS onto it and set it up to become the boot drive.

A 256 or 512gb drive would do fine. No need to spend the $$$ for a 1tb drive.
The internal fusion drive will still work well for storage of "large libraries" (such as movies, music and pictures). Everything else (OS, apps, accounts) can run from the SSD.

If he doesn't already have too much space consumed on the fusion drive, he could use CarbonCopyCloner to "clone over" the contents of the internal fusion drive to the new external SSD.

Be aware that some "prepackaged, ready-to-use" USB3 SSDs will come with factory-installed software that may "get in the way" of the Mac OS. That's why it might be necessary to "clean off" this software first and then re-initialize (i.e., "erase") the drive to Mac format.

Don't spend the extra money for thunderbolt.
I wouldn't worry too much about the lack of TRIM with USB3, either.
 

nambuccaheadsau

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Oct 19, 2007
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Agreed.

When I ran this external TB drive on a 2011 iMac, used the internal for backups and the OP would need to clone the current operating system to thew SSD, connect it up and choose it as the Boot Drive in System Preferences > Startup Disk.

And cloning will be from a 1TB FD which will not run HS at this stage. I would not recommend running the external with one format and the internal as another.
 
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casperes1996

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When I ran this external TB drive on a 2011 iMac, used the internal for backups and the OP would need to clone the current operating system to thew SSD, connect it up and choose it as the Boot Drive in System Preferences > Startup Disk.

And cloning will be from a 1TB FD which will not run HS at this stage. I would not recommend running the external with one format and the internal as another.
There's no need to clone the OS onto the new drive. You can do a fresh install without cloning it, and move the necessary data by hand. Cloning is a possibility, but not a requirement.

A know what you meant btw, but HS does run on the FD. APFS does not. – And there's nothing wrong with running the two drives under different formats, assuming you don't want to use the APFS drive on an older OS. Format the external as APFS, install macOS copy over the data you want on the SSD and keep the Fusion Drive as HFS+. That setup is perfectly valid. If you go for cloning, yes, I recommend keeping them the same format, but otherwise, no issues.
 
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-Ryan-

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Thank you for the advice all. I have now seen the computer in person and can confirm it is actually a 2017 iMac 27" base model with an upgraded 32GB of RAM as opposed to a 2016. This means that USB-C is an option. I have looked at the Fusion Drive specs and it is indeed one with only 24GB of solid state storage. Looking at it myself, it does seem to run very slowly.

He has now ordered one of these: https://www.amazon.co.uk/WD-256-Pas...2WQM/ref=sr_1_1?ie=UTF8&qid=1513724255&sr=8-1

This drive is SSD, USB-C 3.1 gen 2, so hopefully should be the best external solution possible at this price at the moment.

I have read that formatting as AFPS results in extremely slow boot times on external drives - it's unclear whether that's fixed yet, but I think I'll go for HFS+ just in case.
 

alien3dx

macrumors 65816
Feb 12, 2017
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Thank you for the advice all. I have now seen the computer in person and can confirm it is actually a 2017 iMac 27" base model with an upgraded 32GB of RAM as opposed to a 2016. This means that USB-C is an option. I have looked at the Fusion Drive specs and it is indeed one with only 24GB of solid state storage. Looking at it myself, it does seem to run very slowly.

He has now ordered one of these: https://www.amazon.co.uk/WD-256-Pas...2WQM/ref=sr_1_1?ie=UTF8&qid=1513724255&sr=8-1

This drive is SSD, USB-C 3.1 gen 2, so hopefully should be the best external solution possible at this price at the moment.

I have read that formatting as AFPS results in extremely slow boot times on external drives - it's unclear whether that's fixed yet, but I think I'll go for HFS+ just in case.
using that above product for my imac 2017 base model .. :p
 

casperes1996

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Jan 26, 2014
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I have read that formatting as AFPS results in extremely slow boot times on external drives - it's unclear whether that's fixed yet, but I think I'll go for HFS+ just in case.

I did that when High Sierra was in its beta releases cause I didn't want to whipe my internal drive before it was in its final state.... Holy piss it took forever to boot. Has gotten progressively better, but last I tested (10.13.1) it was still not exactly fast compared to HFS+
 

alien3dx

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Feb 12, 2017
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Are you using it as your boot drive? If so, have you formatted as AFPS and does it work properly? Thanks.
as working fine.. but not much diff .. not format to AFPS since i don't see it upon installation upgrade..
Working properly.. i'm using it now.
 

Fishrrman

macrumors Core
Feb 20, 2009
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OP:

My advice is that when you set up the external SSD, DO NOT initialize it using APFS.
Use regular HFS+ (with journaling enabled) instead!

There don't seem to be any real-life benefits to APFS at this point (other than that "it's new") and many users are complaining about it.
 

Bradleyone

macrumors regular
Jul 7, 2015
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Sydney, Australia
One benefit:

I regularly clone my internal drive to an external Samsung T5 SSD (USB 3.1 gen 2) using Carbon Copy Cloner.

Both are formatted with APFS.

Doing so lets CCC make a virtually identical copy that is bootable using the same dark magic boot files on each. (Tip: install High Sierra on the external when first setting up the drive.)

It means I can test installations and changes on the external and know they’re going to work in the internal, and/or clone it back and have an identical copy.

Going APFS internal to HFS+ external would be more problematic for those cases.
 

-Ryan-

macrumors 68000
Original poster
Jan 28, 2009
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I have now installed the MyPassport SSD. For anyone interested, here are the steps I took:

  1. Connected the external SSD to the iMac via USB-C.
  2. Used Disk Utility on the iMac to format the SSD as Mac OS Extended (Journaled) with GUID partition map.
  3. Downloaded High Sierra and installed Mac OS onto the external SSD. This step could be replaced by doing a drive clone using Carbon Copy Cloner or similar software, but a. I don't have a licence and b. my friend wanted to set up the OS from scratch.
  4. Logged on to the external drive copy of Mac OS. This was immediately notably faster than the Fusion Drive.
  5. Went to System Preferences > Startup Disk and chose the external drive as the startup disk.
  6. Copied across all files to keep from the Fusion Drive. Most of this step was unnecessary as iCloud had most files stored in the cloud.
  7. Used Disk Utility to erase the Fusion Drive.
  8. Set up the Fusion Drive as a Time Machine backup location.
  9. Used Velcro strips to mount the SSD to the back of the iMac.
Overall it took around 2 hours. Not difficult and the speed improvements are considerable. It doesn't feel as fast as my 2017 iMac with internal SSD, but it's not much slower. Certainly a recommended upgrade if stuck with the 1TB Fusion Drive with only 24GB of SSD storage.

Thanks for the help everyone.
 

greenbergs

macrumors newbie
Feb 27, 2018
1
0
The Samsung portable SSD requires a password every time you use it. Can you get rid of that function, or does this process override it?
Thanks.

So, a friend has asked me for advice with his 27" iMac. He bought it with a fusion drive, but is looking to go full SSD due to the relatively slow performance. I have explained that the iMac cannot have the drive replaced without some serious surgery on the system and he isn't keen to go that route as it is still in warranty for another 2 years.

I understand it should be possible to boot from a SSD connected via Thunderbolt or USB 3. I've got a few questions about this.

1. Will only specific drives do this or can I buy any enclosure or external drive and it will work?
2. Which is better for this - Thunderbolt or USB 3?
3. What sort of performance improvement would be achieved over the stock 1TB Fusion Drive with a current generation SSD (connected via Thunderbolt or USB 3)?
4. Has anyone done this long term? Any pros or cons?

Thanks in advance!

EDIT: See my later post for steps taken to upgrade to external SSD.
 

mmackinven

macrumors newbie
Jun 28, 2011
10
4
Auckland
I'm looking at doing the same thing to my 2017 iMac 4.2Ghz model.

Does anyone here happen to have Geekbench scores for before and after the conversion to external SSD?
 
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Fishrrman

macrumors Core
Feb 20, 2009
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greenbergs wrote:
"The Samsung portable SSD requires a password every time you use it. Can you get rid of that function, or does this process override it?"

I'm going to -guess- that the Samsung SSD came with some proprietary software/drivers on it (such as for encryption, a password, etc.), and that this drive may even have a proprietary partition on which this software "lives".*

What I believe you need to do runs something like this:
1. Go to Samsung and download their drive management software (not sure what they call it).
2. Use the drive management software to REMOVE the proprietary partition/software
3. Once it's gone, ERASE THE ENTIRE DRIVE using Disk Utility (of course, you'd better BACK IT UP first)
4. Now, with the drive in Mac format/GUID partition map (with no "Samsung software" remaining), RESTORE from your backup drive.
5. That should get rid of the Samsung software/partition and make the drive a "true Mac formatted drive". It should then behave like any Mac drive.

* I don't own a Samsung external SSD, so I don't know what it comes with "from the factory". However, I did have prior experience at this with a Sandisk USB flashdrive bought long ago. It came with a proprietary partition that even Disk Utility couldn't remove (they called the proprietary software "U3"). I actually had to take it back to where I bought it (Circuit City, remember them?), and have the U3 software partition removed using a Windows PC. After that, I was able to reformat the drive using Disk Utility and it still works today.
 
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pvtiste

macrumors newbie
Apr 10, 2018
1
0
I'm looking at doing the same thing to my 2017 iMac 4.2Ghz model.

Does anyone here happen to have Geekbench scores for before and after the conversion to external SSD?
I don't have that but quick test with MS office word : it took around 30s to open it...
Now with my Samsung SSD T5 1 tera it takes 4s.

I was tired with my slow 1 tera fusion drive... Now it's fast :)
 

goutammajumder

macrumors newbie
May 1, 2018
1
0
I have now installed the MyPassport SSD. For anyone interested, here are the steps I took:

  1. Connected the external SSD to the iMac via USB-C.
  2. Used Disk Utility on the iMac to format the SSD as Mac OS Extended (Journaled) with GUID partition map.
  3. Downloaded High Sierra and installed Mac OS onto the external SSD. This step could be replaced by doing a drive clone using Carbon Copy Cloner or similar software, but a. I don't have a licence and b. my friend wanted to set up the OS from scratch.
  4. Logged on to the external drive copy of Mac OS. This was immediately notably faster than the Fusion Drive.
  5. Went to System Preferences > Startup Disk and chose the external drive as the startup disk.
  6. Copied across all files to keep from the Fusion Drive. Most of this step was unnecessary as iCloud had most files stored in the cloud.
  7. Used Disk Utility to erase the Fusion Drive.
  8. Set up the Fusion Drive as a Time Machine backup location.
  9. Used Velcro strips to mount the SSD to the back of the iMac.
Overall it took around 2 hours. Not difficult and the speed improvements are considerable. It doesn't feel as fast as my 2017 iMac with internal SSD, but it's not much slower. Certainly a recommended upgrade if stuck with the 1TB Fusion Drive with only 24GB of SSD storage.

Thanks for the help everyone.
Hello Ryan,

Used Velcro strips to mount the SSD to the back of the iMac - Can you please send me the link how you have done it.

Regards
Goutam
 
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