Installing MacOS on external USB 3 SSD

mrochester

macrumors 68000
Original poster
Feb 8, 2009
1,882
359
Hi all

I was looking at an iMac but perhaps getting one with a standard hard drive and then using an external USB 3 connected SSD to install MacOS onto.

Does anyone have any experience of how well this will work? I understand that there is a theorietical maximum throughput for USB 3 that you rarely achieve but would this impact performance significantly? The thing I appreciate most about SSDs is the reduced latency rather than the increased throughput so would USB 3 impact this to make it not worthwhile?

Many thanks

M.
 

BrianBaughn

macrumors 603
Feb 13, 2011
6,347
934
Baltimore, Maryland
I assume you mean the 21.5 inch iMac without a fusion drive.

The drive is the slowest thing on a computer these days and there's really no excuse to be running the system on anything other than an SSD (or at least a fusion drive) connected to the fastest available bus on the unit.

It seems like the cheapest iMac available is never a great choice.
 
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keysofanxiety

macrumors G3
Nov 23, 2011
9,468
24,217
It'll work very well. SSD real-world performance boost predominantly come from the instant access times, so a slight deficit in read/write speeds won't have much noticeable effect, especially if you're used to HDD performance!

Also couldn't be easier to set up:

1) plug in SSD via USB
2) hold CMD + R on startup
3) format SSD in disk utility
4) select reinstall macOS & point it to the SSD
5) laugh maniacally at the ease of drastically improving system performance (optional)
 

Fishrrman

macrumors P6
Feb 20, 2009
17,170
5,526
OP wrote:
"I was looking at an iMac but perhaps getting one with a standard hard drive and then using an external USB 3 connected SSD to install MacOS onto."

My advice is "don't do this".
Spend $100 more and get the iMac with the 256gb SSD (you have to do this through "build to order").

The internal SSD will be 4-5x faster than any external SSD. VERY fast.

I recommend booting from an external SSD for older Macs, but the new iMacs have such a great internal SSD it's the best option.
And did I mention that you can get the 256gb version for only $100 more?