Speeds booting from external SSD via USB 3.0?

[dictoresno]

Going to get a 250-480 GB SSD at some point to replace the 1TB spinner in my 2015 iMac. Now I currently have a USB 3.0 compatible dual drive docking station and also a single drive inatek USB 3.0 enclosure. If I were to mount a new SSD in the enclosure and plug it in via USB cable, I would imagine my speeds would be much better than the internal spinner. I ran a test on my current drive and I'm getting a normal 98-102 MB/s read and write speeds. Would an external SSD connected via USB 3 offer me close to the same speeds vs an internal mounted one? They don't seem to make a single drive thunderbolt enclosure, so I guess that's out of the question.

Bottom line is I'm looking to run my machine and boot into macOS from the external SSD only and then use the 1 TB internal as extra storage. Anyone else doing this and how much slower would it be vs internally mounted. Is this a viable option vs mounting the boot disk internally?

Because of the difficulty in having to separate the screen, I would prefer NOT to take apart my brand new 2015 iMac to replace the internal drive if I don't have to since I'm still under warranty.

Extra points for being able to boot from external SSD but have the external continuously being mirrored to the internal drive in case I needed to unplug the external and boot from the internal spinner as well and have all my stuff in tact.

 

[keysofanxiety]

The speeds won't be as consistent compared to SATA, but it'll still run very quickly and make a massively positive difference to the performance.

 

[maflynn]

I'm rocking with an external SSD for my OS X usage (my internal drive has Windows), and I find it plenty fast. Much faster then a spinning drive. I'm happy with the performance.

One downside of an external drive is the lack of TRIM. I don't know if or when that will impact me, but so far performance has been great.

 

[Fishrrman]

OP wrote:
"I ran a test on my current drive and I'm getting a normal 98-102 MB/s read and write speeds. Would an external SSD connected via USB 3 offer me close to the same speeds vs an internal mounted one?"

With an SSD mounted in a USB3 external enclosure or dock (one that is specifically advertised to support "UASP"), you should get reads around 430mbps and writes from 250-350+mbps.

The write speed will be more dependent upon the capabilities of the particular SSD you buy, rather than the enclosure/dock.

So... it's reasonable to expect to see a 4x increase in read speeds if you go USB3 enclosure or dock. Along with 2-3x (or greater) increase in write speeds.

OP also wrote:
"Bottom line is I'm looking to run my machine and boot into macOS from the external SSD only and then use the 1 TB internal as extra storage. Anyone else doing this and how much slower would it be vs internally mounted. Is this a viable option vs mounting the boot disk internally?"

Of course.
Doing this will "change your world" -- so much so that you won't believe it until you've tried it.

Since you already have both an enclosure and a dock, I suggest you do this:
1. Get the SSD of your choice. My opinion only, but I would advise you to AVOID Samsung drives and get either a Crucial or Sandisk drive instead.
2. Initialize the drive using Disk Utility (HFS+ with journaling enabled)
3. Now, either install a fresh copy of the OS onto it, or -- use CarbonCopyCloner to "clone over" the OS from the internal drive. Note: you can set up CCC to clone the recovery partition as well, and if space is a consideration, you can set up CCC to "selectively clone" only the OS while you "leave some things behind", if they consume too much space.
For example, I would leave "large libraries" (music, pictures, movies) on the HDD, with "stripped down" accounts on the SSD.
The goal here is to keep the boot SSD running "lean and clean".

Once you're done, try booting the iMac from both the enclosure AND the dock. Do a speed test each way. One may yield better speeds than the other. I would then go with "the fastest", insofar as read speeds are concerned. For most usage, write speeds are more important than write speeds.

DON'T be overly concerned about TRIM.
I've been booting and running my late 2012 Mac Mini for FOUR YEARS from an SSD mounted in a USB3/SATA docking station. It runs as fast today as when I first booted it, and TRIM has NEVER been enabled.
TRIM is (for all practical purposes) a non-issue.
Those who deride using a USB3 "external booter" have NO real-world experience booting and running via USB3 over any period of time...

 

[CoastalOR]

I did a Black Magic speed test on a new Samsung 850 EVO 500GB in a USB3 Inateck enclosure. The results were 378.6 MB/s Write and 427.6 MB/s Read.

 

[dictoresno]

LOL I just did a speed test on my internally mounted 240 GB Kingston SSD in my 2010 MBP, 6GB RAM and a 2.53 GHz Intel Core i5. This is terrible LOL! I was considering removing it from the MBP and using it in the enclosure for the iMac in question.

Are these speeds due to the old hardware the drive it mounted to?

 

[kschendel]

It might be worth going to System Profiler and checking what your negotiated SATA link speeds are to the SSD.

 

[dictoresno]

I ended up buying the 480 GB SSD which ill mount externally and run my main OS.
[doublepost=1484796884][/doublepost]

It might be worth going to System Profiler and checking what your negotiated SATA link speeds are to the SSD.

heres what system info says.....

Vendor: Intel
Product: 5 Series Chipset
Link Speed: 3 Gigabit
Negotiated Link Speed: 3 Gigabit
Physical Interconnect: SATA
Description: AHCI Version 1.30 Supported



KINGSTON SUV400S37240G:


Capacity: 240.06 GB (240,057,409,536 bytes)
Model: KINGSTON SUV400S37240G
Revision: 0C3FD6SD
Native Command Queuing: Yes
Queue Depth: 32
Removable Media: No
Detachable Drive: No
BSD Name: disk0
Medium Type: Solid State
TRIM Support: No
Partition Map Type: GPT (GUID Partition Table)
S.M.A.R.T. status: Verified

 

[Weaselboy]

Are these speeds due to the old hardware the drive it mounted to?

Yep... that's the issue. Your 2010 has only SATA II and not the faster SATA III connection of newer Macs.

 

[dictoresno]

oh well.

I actually think I'm gonna go ahead and internally mount the SSD. Ive been watching the videos and they actually don't seem too bad. Bought the resealing adhesive kit for $9.99.

 

[kschendel]

The write speed looks a bit low even for SATA II, but the read speed isn't all that far off. You might possibly try booting from the recovery partition and doing a filesystem verify/repair on the internal SSD.

 

[macmee]

I have this SSD:

Samsung SSD 750 EVO 500GB

I have this USB 3.0 enclosure:

Inateck 2.5 Inch USB 3.0 Hard Drive Disk Enclosure/ Case for 9.5mm 7mm 2.5 Inch SATA I/II/III/HDD/SSD, Support UASP and Optimized For SSD, Tool-Free

and it runs faster than a new version of anything by Microsoft needing to be patched:

You can also max out the SATA 3 performance bottleneck (is that even right lol?) of your drive if you go for a thunderbolt enclosure instead, but those cost more money. Personally I think these speeds are great with the Inateck!

 

[dictoresno]

I have the Inateck FE2004 model, works great.