iMac - External SSD as a boot drive?

TomOSeven

macrumors 6502
Original poster
Jul 4, 2017
357
391
Hi all,

I have an iMac 5k from 2017 which I love, but it's the base model with a Fusion Drive.

Is there an easy way to permanently use a USB-C SSD as a boot drive?

Could I just do Time Machine Backup, connect a USB-C SSD, boot into recovery and install OSX anew based on the backup, onto the USB-C drive?

Thanks!
 

tomscott1988

macrumors 6502a
Apr 14, 2009
620
483
UK
Answered your own question :)

Other way is to use something like Carbon Copy Cloner, or install a new copy of Mojave onto the SSD and use migration assistant to move your files over. All very user friendly. Not really much need to use time machine.

Just set the external as the preferred boot option in System preferences and your good to go.
 

ukp

macrumors member
Feb 9, 2007
31
4
As above, yeah you can. I use a Samsung T5 SSD on one of my imacs and it exclusively uses the external drive for booting and general day to day use. My internal drive is now used for time machine.
 
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mikehalloran

macrumors 68000
Oct 14, 2018
1,752
454
The Sillie Con Valley
Hi all,

I have an iMac 5k from 2017 which I love, but it's the base model with a Fusion Drive.

Is there an easy way to permanently use a USB-C SSD as a boot drive?

Could I just do Time Machine Backup, connect a USB-C SSD, boot into recovery and install OSX anew based on the backup, onto the USB-C drive?

Thanks!
Bad idea. USB is too slow. You can’t enable TRIM. Other issues.

A Samsung X5 is 6x faster over Thunderbolt 3. Boot from that and you’ll have the same performance as if you bought an SSD iMac.

To use the internal HDD for Time Machine, you’ll have to untie if from the SSD and format it Extended GUID but certainly doable.

There are a number of recent threads that ask this same question. I went into greater detail in those.
 

tomscott1988

macrumors 6502a
Apr 14, 2009
620
483
UK
TBH for 90% of people a USB SSD is ideal. The X5 is 4 times the price and for most people the performance day to day wont be noticeable, 3000mb/s r/ws is great but way overkill for most people.
A sata 3 ssd over USB 3.1 gen 2 is a cheap way to make you Mac feel infinitely more responsive. In all honesty trim isn't the end of the world either. Myself and others have had these set up for years with minimal differences in performance.

Recently I bought a Thunderbay 6 from OWC and have a 1TB Samsung Evo 970+ M2 NVME over TB installed which runs 3000mb/s r/ws day to day use it feels almost the same as the 3.1 1tb budget SanDisk ultra 1TB I had before. Boots are near identical, program launches are similar.

Its only when you are exporting large video files or big transfers where it is noticeable and a bottle neck but really that more advanced.

Otherwise 550mb/s is more than adequate for 4k video and any other day to day task. 1TB ssds can be had for £80 and a 3.1 usb c caddy £20 so £100 vs £420 for the X5.

Or you could buy a T5 for £170 but they perform very similar to a build at home variant.
 

Fishrrman

macrumors Core
Feb 20, 2009
19,700
6,869
USB-c SSD will make a fine external boot drive. You should get reads of about 430mbps and writes in the 350-375mbps range.

IF your fusion drive isn't "too full" yet, and IF all the contents will fit onto the SSD, the fastest way to accomplish this is:
1. Connect new SSD and use Disk Utility to format it to Mac format (either HFS+ or APFS)
2. Download CarbonCopyCloner from here:
http://www.bombich.com/download.html
(CCC is FREE to download and use for 30 days)
3. Launch CCC and clone the contents of the internal to the new SSD
4. When done, go to the startup disk pref pane and choose the SSD to be the boot drive
5. Reboot.
6. Done.

ONE MORE THING:
If you'd like more speed, you could get one of the these two solutions:

First solution:
Samsung X5 thunderbolt drive.
VERY VERY fast (will far outperform ANY fusion drive), but these are considerably more $$$$.

Second solution:
Get a "bare" nvme blade drive (MUST be "nvme")
Get a USB3.1 gen2 enclosure, such as this:
https://www.amazon.com/gp/product/B07N48N5GR/ref=ppx_yo_dt_b_asin_title_o00__o00_s00?ie=UTF8&psc=1
Put the drive into enclosure and set it up (same as above). Just click the button to open and "drop the drive inside".
This will give you read speeds up around the 850-900mbps range.
Not as fast as thunderbolt, but almost twice the speed of USB3.1 gen1.
And the cost is VERY reasonable for the additional speeds you'll get.
 
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LLA

macrumors newbie
May 23, 2019
8
1
Los Angeles
Bad idea. USB is too slow. You can’t enable TRIM. Other issues.

A Samsung X5 is 6x faster over Thunderbolt 3. Boot from that and you’ll have the same performance as if you bought an SSD iMac.

To use the internal HDD for Time Machine, you’ll have to untie if from the SSD and format it Extended GUID but certainly doable.

There are a number of recent threads that ask this same question. I went into greater detail in those.
Hey, miehalloran, I was told by apple and OWC (where I bought an enclosure in order to use my SSD to run the new iMac, that the thunderbolt connection would not make for a faster set up because the SSD speed (or whatever drive one has) is what dictates speed. The connection cannot make things faster than the drive itself. Do you concur?
 

jharvey71884

macrumors 6502
May 3, 2011
286
24
2015 iMac owner here. Been using USB 3 Samsung SSD boot driver for two years. Did the same thing for 2013 iMac. Don’t listen to anyone that says it is a bad idea. More than adequate over fusion drive.

Used a zip tie or two and mounted to iMac base.
 

SaSaSushi

macrumors 601
Aug 8, 2007
4,104
497
Takamatsu, Japan
I would not recommend booting from a USB3 drive on a 2017 or later iMac with TB3.

The Shell Thunderbolt NVME enclosure can be purchased for $151 and coupled with the NVMe SSD of your choice. Performance apparently matches that of the Samsung X5, depending on the SSD, at a lower price.

More products will continue to be released and prices will only continue to drop.
 
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smirk

macrumors 6502a
Jul 18, 2002
678
47
Orange County, CA
Hey, miehalloran, I was told by apple and OWC (where I bought an enclosure in order to use my SSD to run the new iMac, that the thunderbolt connection would not make for a faster set up because the SSD speed (or whatever drive one has) is what dictates speed. The connection cannot make things faster than the drive itself. Do you concur?
It is correct that the connection won't make things faster than the drive itself, but what you may not be aware of is that there are two different types of SSD drives.

SATA SSDs look like a mini hard drive and use the same connectors as hard drives. They are faster than mechanical hard drives, maybe 500 MB/second as opposed to ~100 MB/s for a mechanical. These are ballpark numbers, I'm not an expert on drive speeds.

NVMe SSDs look like a really long memory stick, and basically plug directly into a PCIe slot. They are much faster than SATA SSDs, maybe 1,500 - 3,000 MB/s.

There is also something called TRIM, which is a process that cleans up unused blocks on an SSD. macOS does not support TRIM over USB but does over Thunderbolt, which is why people are recommending the use of Thunderbolt for external drives instead of USB.

There seems to be two schools of thought on the TRIM issue. @Fishrrman believes that TRIM functionality isn't critical and that using a less expensive USB drive works perfectly well. @mikehalloran believes that Thunderbolt should be used for a faster connection and TRIM support.

You may find this article interesting/helpful:
https://www.theverge.com/2019/5/13/...rbolt-3-usb-c-samsung-x5-t5-specs-test-how-to
 
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faraway52

macrumors member
Mar 3, 2019
32
10
Germany
I have two 2TB X5 connected via TB3 to my iMac 2017. It is very fast and more expensive than the iMac
BUT
you should go with a nice SATA SSD connected via USB 3 adapter if you have no hard facts to spend all the X5 money.

ps. Yes you will have no Trim but how much $$$$ are you going to save and what will Trim do for you and your way of using the iMac?
pps. Just plug the USB drive in, format it and run CCC and you are done. It is that simple.
 
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Blondie88

macrumors newbie
Jul 2, 2019
6
0
Is anyone experiencing problems running Mojave off a SSD boot disk? I was just about to buy an external SSD to use as a boot for my new iMac but read that people were experiencing problems with Mojave and slow boot up times. Can anyone advise?
 

Blondie88

macrumors newbie
Jul 2, 2019
6
0
Not at all. I boot and run Mojave from both external TB3 attached Samsung X5 2TB SSDs,
Thanks for the reply. The comments I had been reading were from 2018 I believe, so hopefully it's something that has been rectified now. Hope the same is true of the standard Samsung T5 drives.
 

smirk

macrumors 6502a
Jul 18, 2002
678
47
Orange County, CA
There was an issue that seemed to be related to booting a Mac from a USB SSD when it was formatted as APFS. The issue was that bootups would take a long time, sometimes a few minutes (it would hang for 1-3 minutes before starting to load the OS). However, Apple seems to have fixed this -- although I personally can't verify it as I don't boot from an external SSD anymore.
 

Blondie88

macrumors newbie
Jul 2, 2019
6
0
There was an issue that seemed to be related to booting a Mac from a USB SSD when it was formatted as APFS. The issue was that bootups would take a long time, sometimes a few minutes (it would hang for 1-3 minutes before starting to load the OS). However, Apple seems to have fixed this -- although I personally can't verify it as I don't boot from an external SSD anymore.
thanks for the reply
 

MacRumorUser78

macrumors newbie
Jan 9, 2014
26
8
OWC Envoy Pro EX 2TB, Performance Up to 2800MB/s, Drive Interface M.2 NVMe (PCIe 3.0) at $480
vs
Samsung Portable SSD X5 MU-PB2T0B at $722 with seemingly the same specs NVM Express (NVMe) and 2800 MB/s.

Looking to use with 2017 27: iMac which currently has 2TB Fusion Drive which seems to be the slowing things down.

Is OWC reliable or am I missing something?
 

cynics

macrumors G4
Jan 8, 2012
11,586
1,886
Time your Mac's start up.

Most of the OS resides on the SSD portion of the fusion already. Start up from an HDD is around 1 minute 30 seconds and you still have some time while everything is "settling in". Conversely if your boot is 10-15 seconds than moving to a USB SSD will likely result is lower OS performance.

While many people are perfectly happy with the results, personally I'm not a fan of USB SSD's for the OS or system files with a Mac due to lack trim and the amount of write amplification it causes.

Now that SSD's are cheap I use them for scratch disk and temp files via USB using a USB to SATA adaptor. I could always feel performance degradation so I would just format it and back to the races. This time I collected some data.

The set of images are collected from AmorphousDiskMark for a 240gb Sandisk SSD. First picture is a just after a clean format, second picture is 80% full drive but I've been deleting stuff off it so its technically full., 3rd image is disk utility showing I deleted EVERYTHING off (deleted not format), 4th is a speed test after showing that obviously my Mac not telling the SSD what is junk makes a difference.

Format and expired.png


Screen Shot 2020-08-01 at 3.40.31 AM.png



These were taken the same time as the above images except using black magic instead. 1. Is fresh format. 2. 80% full. 3. is Disk utility 4. is the test after manually wiping (not formatting).

Screen Shot 2020-08-01 at 2.56.52 AM.png


Screen Shot 2020-08-01 at 3.43.16 AM.png


As you can see write speed takes a massive 210 - 220 MB/s hit with sequential writes leaving me with worse than HDD performance. Keep in mind I'm not comparing the SSD's speed because I know its not the fastest but I'm comparing the loss in performance.

Thats my personal experience anyway, if anyone has any tips aside from formatting them once every week or 2 I'm more than open to suggestions.

Regardless based on that is why I always preferred installing an SSD in a Mac (if that is even possible anymore). My internal is 85-90% full and its been installed for 3 years....

Samsung860-81-20.png
iMac SamsungSSD.png
 

Fishrrman

macrumors Core
Feb 20, 2009
19,700
6,869
MacRumorUser:

Use blackmagic speed test (or another drive benchmark utility), and post the results you get here.

What read/write speeds are you getting RIGHT NOW?
 
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