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Dru Nemeton

macrumors newbie
Original poster
Nov 30, 2019
5
0
GGNRA
Salutations!

Foreword:
My unending thanks to the contributors of these forums that answer posts in an informative and non-judgemental manner. Your experience and guidance was instrumental in bringing me up to speed on making some 'big ticket' purchases. Thank You!!!

Bottom Line:
Is a BlackMagic benchmark on the base model 2017 iMac (imac18,1 with 1TB HDD) of about 450Mb/s for read/writes "as good as it can get"?

Background:
I have the base model, mid-2017 iMac (imac18,1) and as I understand it since the iMac didn't come with any form of SSD factory-installed it lacks the necessary internal hardware to fully support the Thunderport 3 port speeds (40Gb/s).

Since this also can't be added later I'm limited to SATA III speeds (6Gb/s), regardless if it's an internal or external drive.

So during Black Friday sales I snagged a 2TB Samsung SSD and placed it in a USB 3.1 USB-C external enclosure (10Gb/s). I used Carbon Copy Cloner to transfer the 760GB of data on the internal drive to the new external drive formatted as HFS+. The macOS is High Sierra.

Note 1: This took over 10 hours! So do setup CCC to e-mail you once it's done.
Note 2: It wasn't until it was done that it made any mention of the recovery partition. I chose Yes (of course) and it only took a minute to create the partition and copy the data.
Note 3: TRIM was enabled via "sudo" after booting up from the drive and that took about 7 minutes of the iMac just sitting there before it rebooted so be patient.

Postscript:
This upgrade was so worth it! As a proud nerd I'm posting this question just to make sure I'm at as "Peak iMac" as I can be for my model. But if any of you have an iMac with an internal HDD you will not be disappointed by upgrading to an external SSD. I can't believe I waited this long.

I purchased the drive and enclosure at a local store on Black Friday for $204 + change.
 

casperes1996

macrumors 603
Jan 26, 2014
5,985
3,857
Horsens, Denmark
I have the base model, mid-2017 iMac (imac18,1) and as I understand it since the iMac didn't come with any form of SSD factory-installed it lacks the necessary internal hardware to fully support the Thunderport 3 port speeds (40Gb/s).

That is incorrect. It doesn't need anything extra to support full Thunderbolt transfer speeds. Keep in mind 40Gb/s ≠ 40GB/s.

So during Black Friday sales I snagged a 2TB Samsung SSD and placed it in a USB 3.1 USB-C external enclosure (10Gb/s). I used Carbon Copy Cloner to transfer the 760GB of data on the internal drive to the new external drive formatted as HFS+. The macOS is High Sierra.

Which Samsung SSD and which enclosure matters here.

----------------------------------------------------------------

Regardless, for "regular" usage, storage speeds become a game of diminishing returns. From an HDD to any SSD is a massive, very, very noticeable jump for any kind of usage, but it's much less between let's say 450MB/s and 1GB/s. You might not really notice it for "normal" things.
 
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Fishrrman

macrumors Core
Feb 20, 2009
21,498
7,758
Run BlackMagic on the drive.
Post the results.

If it's a 2.5" SSD in a USB3 enclosure, reads will be in the 430MBps range.

Want faster?
Then get an nvme blade drive, and put it into a USB3.1 gen2 enclosure.
That gives reads around 965MBps.

Want even faster than that?
Then put the nvme blade drive into a thunderbolt3 enclosure.
That should boost reads to around 2200MBps or better.
 
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Dru Nemeton

macrumors newbie
Original poster
Nov 30, 2019
5
0
GGNRA
That is incorrect. It doesn't need anything extra to support full Thunderbolt transfer speeds. Keep in mind 40Gb/s ≠ 40GB/s.

Which Samsung SSD and which enclosure matters here.

----------------------------------------------------------------

Regardless, for "regular" usage, storage speeds become a game of diminishing returns. From an HDD to any SSD is a massive, very, very noticeable jump for any kind of usage, but it's much less between let's say 450MB/s and 1GB/s. You might not really notice it for "normal" things.

Sorry for the delay in my reply.

I bought the 2TB EVO SSD and a Comika USB 3 enclosure. Thank you!
[automerge]1576550230[/automerge]
Run BlackMagic on the drive.
Post the results.

If it's a 2.5" SSD in a USB3 enclosure, reads will be in the 430MBps range.

Want faster?
Then get an nvme blade drive, and put it into a USB3.1 gen2 enclosure.
That gives reads around 965MBps.

Want even faster than that?
Then put the nvme blade drive into a thunderbolt3 enclosure.
That should boost reads to around 2200MBps or better.

I did post the results: about 450MB/s read/write speeds. So your comment about USB3 reading about 430MB/s were spot on.

Now I'm just scratching my head because I'm 100% sure that read (either here or www.everymac.com) that if the iMac didn't come with some form of SSD pre-installed it was missing an important piece on the logic board that couldn't be added later and that the missing piece would forever limit how fast external storage would run.

Oh well! It's plenty fast now and if it needs a speed boost later I'll follow your recommendations. Thanks!
 
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casperes1996

macrumors 603
Jan 26, 2014
5,985
3,857
Horsens, Denmark
Now I'm just scratching my head because I'm 100% sure that read (either here or www.everymac.com) that if the iMac didn't come with some form of SSD pre-installed it was missing an important piece on the logic board that couldn't be added later and that the missing piece would forever limit how fast external storage would run.

I feel pretty confident in saying that even if you did read that, it’s just not true. I can think of no component that could legitimately explain that.
 
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mj_

macrumors 65816
May 18, 2017
1,240
809
Austin, TX
I have the base model, mid-2017 iMac (imac18,1) and as I understand it since the iMac didn't come with any form of SSD factory-installed it lacks the necessary internal hardware to fully support the Thunderport 3 port speeds (40Gb/s).

Since this also can't be added later I'm limited to SATA III speeds (6Gb/s), regardless if it's an internal or external drive.
I have no idea where you've got that information from but it's definitely incorrect. Your iMac has full Thunderbolt 3 support. What you're running into is the standard SATA III limit of roughly 500 MB/s (depending on chipset implementation). That, however, has nothing to do with Thunderbolt 3 or your iMac but merely the SATA III specification. If you want higher speeds you will need an NVMe drive in a Thunderbolt 3 case (up to 40 Gb/s), or alternatively an NVMe drive in a USB 3.1 case (up to 10 Gb/s).
 
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Dru Nemeton

macrumors newbie
Original poster
Nov 30, 2019
5
0
GGNRA
I have no idea where you've got that information from but it's definitely incorrect. Your iMac has full Thunderbolt 3 support. What you're running into is the standard SATA III limit of roughly 500 MB/s (depending on chipset implementation). That, however, has nothing to do with Thunderbolt 3 or your iMac but merely the SATA III specification. If you want higher speeds you will need an NVMe drive in a Thunderbolt 3 case (up to 40 Gb/s), or alternatively an NVMe drive in a USB 3.1 case (up to 10 Gb/s).

I think it was the PCIe bridge that's installed with the SSD drive internally, and can't be installed after purchase. For some reason I took that to mean the entire bus was then limited. Quite happy to learn that I'm wrong.

Here's a super quick break down I just found on SATA III actual speed: https://www.howtogeek.com/219685/what-is-the-actual-speed-of-sata-3/. It seems that 600MB/s is the maximum real-world transfer rate from the 6Gb/s

I did a quick test last night and switched my enclosure cables from USB-A>C to USB-C>C and got horrible results in BlackMagic. So the enclosure seems to be performing at spec.

So I'm left with the impression that what I have is indeed "as good as it can get" for the kit that I have. Which is a huge step up from the HDD, and still leaves me with room to 'geek out' in the furture.

Thanks everyone! I'm truly happy to have found such a great community.
 
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macrumors 6502
Nov 21, 2019
333
581
Buy a TB3 case for far better results.

SATA SSDs will always be limited to a max read/write speed of about 500/500 MB/sec, regardless of the enclosure used.
[automerge]1576607136[/automerge]
Here's a super quick break down I just found on SATA III actual speed: https://www.howtogeek.com/219685/what-is-the-actual-speed-of-sata-3/. It seems that 600MB/s is the maximum real-world transfer rate from the 6Gb/s

That's a theoretical speed. 500/500 is the real-world max you will ever see from SATA III. I have a Crucial 2TB installed internally in an iMac and get about 500+ read and 460+ write speeds.
 
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casperes1996

macrumors 603
Jan 26, 2014
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Horsens, Denmark
That's a theoretical speed. 500/500 is the real-world max you will ever see from SATA III. I have a Crucial 2TB installed internally in an iMac and get about 500+ read and 460+ write speeds.

Theoretical speed, before we get into overhead from the protocol, is actually 750MBps, but that's just an aside, carry on as you were :)
 
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casperes1996

macrumors 603
Jan 26, 2014
5,985
3,857
Horsens, Denmark
Hmm. Not sure about the math, but that's not what I have seen in discussions online.

A byte is 8 bit. 6Gb/s is 6giga-bits per second. 6 billion / 8 gives you bytes per second. 6 billion / 8 = 750 million bits, = 750MB/s. - What you've seen may take protocol overhead into account or other things like that before calculating the theoretical. I can assure you the math is correct though, 6Gb/s = 750MB/s.
 
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||\||

macrumors 6502
Nov 21, 2019
333
581
A byte is 8 bit. 6Gb/s is 6giga-bits per second. 6 billion / 8 gives you bytes per second. 6 billion / 8 = 750 million bits, = 750MB/s. - What you've seen may take protocol overhead into account or other things like that before calculating the theoretical. I can assure you the math is correct though, 6Gb/s = 750MB/s.

OK.
 
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Dru Nemeton

macrumors newbie
Original poster
Nov 30, 2019
5
0
GGNRA
Hmm. Not sure about the math, but that's not what I have seen in discussions online.

From my earlier link:
“While data is actually sent at 6 Gb/s, it is encoded to counteract two common defects in telecommunications, DC Bias and Clock Recovery. This is often accomplished using a specific coding algorithm called 8b/10b Encoding. It is not the only encoding algorithm which has been devised to this end (there is also a Manchester encoding), but it has become the de facto standard for SATA data transfer.

In 8b/10b encoding, eight bits of signal are replaced by 10 bits of (signal + code). This means that, out of the 6 Gb the channel sends in a second, only 8/10 (4/5) are signal. 4/5’s of 6 Gb is 4.8 Gb, which in turn equals 600 MB. This is what degrades the 6 Gb/s channel into a mere(?) 600 MB/s channel.”
 
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macrumors 6502
Nov 21, 2019
333
581
From my earlier link:
“While data is actually sent at 6 Gb/s, it is encoded to counteract two common defects in telecommunications, DC Bias and Clock Recovery. This is often accomplished using a specific coding algorithm called 8b/10b Encoding. It is not the only encoding algorithm which has been devised to this end (there is also a Manchester encoding), but it has become the de facto standard for SATA data transfer.

In 8b/10b encoding, eight bits of signal are replaced by 10 bits of (signal + code). This means that, out of the 6 Gb the channel sends in a second, only 8/10 (4/5) are signal. 4/5’s of 6 Gb is 4.8 Gb, which in turn equals 600 MB. This is what degrades the 6 Gb/s channel into a mere(?) 600 MB/s channel.”

You are never going to get that speed in real world application. SATA III is bottle necked at about 500 MB/sec.
 
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