External SSD faster on iMac...I wonder why?

[hakr100]

I have a new MBA M1 and a new Samsung SSD Model T7. Almost nothing on either drive. External SSD is plugged directly into the MBA. I am getting 650 MB/s on writes with the Samsung and 694 MB/s with reads.

I then plugged the Samsung T7 into my 2020 iMac and got 900 MB/s writes and 916 MB/s reads, significantly faster - about one-third faster -than the same drive on my new MacBook Air.

Both tests with the cable supplied by Samsung. The internal and portable drives are formatted APFS. Tests run with the Black Magic Disk Speed Test.

Any ideas why the Samsung drive is about one third faster when plugged into the iMac?

 

[bobcomer]

You might try switching ports between the power and the T7, I've seen stranger things, but I've seen the speed of things plugged into the M1 Mac being slow all over the place here. I haven't personally tested a SSD, but I know ethernet plugged into my M1 MBA's port is slower than the same USB Nic plugged into anything else I have. Not painfully slow, but annoying slow level.. Why, I have no idea.

 

[hakr100]

Thanks, bobcomer. I did try that, and it made no difference. A tech guy at Samsung said he thought Apple might not have done a "good job" coding whatever makes the ports on the M1 work at the proper speeds with SSDs. As a point of info, I get the same speeds with my USB ethernet plugged into the M1 as I do with my iMac. Go figure.

 

[BrianBaughn]

In one of the Max Tech videos he demonstrates that on the M1 Macs some drives are faster going through an OWC hub than plugged in directly.

 

[joevt]

Read this thread https://forums.macrumors.com/thread...ally-10gb-s-also-definitely-not-usb4.2269777/
The solution is to use a different USB controller by connecting a Thunderbolt device with USB ports or a second Thunderbolt port.

 

[Slartibart]

Any ideas why the Samsung drive is about one third faster when plugged into the iMac?

It’s a T7...it is fast. 🤓 Seriously: the T7 offers quite a lot for their price.

 

[Significant1]

If I am not mistaken, it is because your drive support usb 3.2 10gbps, while m1 is usb 4 and usb 4 does not support 3.2 10gbps. USB 4 does have a 10gbps mode, but it is not electrical compatible with 3.2gbps. the work-around is a thunderbolt dock with usb 3.2 10gbps support, else you are connected at "only" 5gbps.

USB4 - Wikipedia

en.wikipedia.org

 

[joevt]

If I am not mistaken, it is because your drive support usb 3.2 10gbps, while m1 is usb 4 and usb 4 does not support 3.2 10gbps. USB 4 does have a 10gbps mode, but it is not electrical compatible with 3.2gbps. the work-around is a thunderbolt dock with usb 3.2 10gbps support, else you are connected at "only" 5gbps.

USB4 - Wikipedia

en.wikipedia.org

Are you talking about Gen 1x2 (two lanes of 5 Gbps)?

The T7 supports Gen 2x1 (one lane of 10 Gbps), same as the M1 Mac.

Some USB4 hosts may support Gen 1x2 and Gen 2x2 (two lanes of 10 Gbps) but not the M1 Mac.

hakr100 was able to get 694 MB/s which means he is getting greater than 5 Gbps, so the connection is working at 10 Gbps but the performance is lower than expected for Gen 2x1.

 

[Significant1]

Are you talking about Gen 1x2 (two lanes of 5 Gbps)?

The T7 supports Gen 2x1 (one lane of 10 Gbps), same as the M1 Mac.

Some USB4 hosts may support Gen 1x2 and Gen 2x2 (two lanes of 10 Gbps) but not the M1 Mac.

hakr100 was able to get 694 MB/s which means he is getting greater than 5 Gbps, so the connection is working at 10 Gbps but the performance is lower than expected for Gen 2x1.

Ok, Just checked T7, Samsung is not completely clear about that. They state:
USB 3.2 Gen.2 (10Gbps)
and that could be 1x2 or 2x1 as far as I am concerned.

Must be 2x1 to match Apple's USB 3.1 gen 2 10Gb/s specification.

 

[hakr100]

Heh heh. I'm not laughing at you guys, but at the general confusion created by vendors and standard setting organizations. The answer here seems to be that if I buy a Thunderbolt dock of a certain unspecified specification, I might or might not see an increase in speed on my Samsung T7 external drive. Since the drive operates a third faster when plugged into my iMac, I am unscientifically concluding the issue lies with the MacBook Air and not the drive. Or maybe not. 🧏‍♂️

 

[Significant1]

Heh heh. I'm not laughing at you guys, but at the general confusion created by vendors and standard setting organizations. The answer here seems to be that if I buy a Thunderbolt dock of a certain unspecified specification, I might or might not see an increase in speed on my Samsung T7 external drive. Since the drive operates a third faster when plugged into my iMac, I am unscientifically concluding the issue lies with the MacBook Air and not the drive. Or maybe not. 🧏‍♂️

Yeah, the usb naming standard is a mess, mainly because they rename old standards!?!, when they introduce a new version. I would have been less confusing, if Samsung had used the old USB 3.1 Gen 2 name (if that is the standard they support), like Apple, or at least specified precisely which usb 3.2 gen 2 they use.

I haven't read the thread linked to earlier, so there might really be a limitation on Apple side. Just wierd, when they plainly state USB 3.1 Gen 2 (up to 10Gb/s) is supported.

 

[joevt]

Yeah, the usb naming standard is a mess, mainly because they rename old standards!?!, when they introduce a new version. I would have been less confusing, if Samsung had used the old USB 3.1 Gen 2 name (if that is the standard they support), like Apple, or at least specified precisely which usb 3.2 gen 2 they use.

I haven't read the thread linked to earlier, so there might really be a limitation on Apple side. Just wierd, when they plainly state USB 3.1 Gen 2 (up to 10Gb/s) is supported.

I agree - I use the earliest spec number for each mode
5 Gbps USB 3.0 (uses 8b/10b -> 4 Gbps)
10 Gbps USB 3.1 gen 2 (uses 128b/132b encoding -> 9.70 Gbps)
10 Gbps USB 3.2 gen 1x2 (uses 8b/10b encoding -> 8 Gbps)
20 Gbps USB 3.2 gen 2x2 (uses 128b/132b encoding -> 19.39 Gbps)

The linked thread has a bunch of examples showing how the M1 Mac USB controller is not as performant as a USB controller ought to be. You can connect other USB controllers via Thunderbolt to get most of the performance back.

Read about 3.2 gen 2x2 testing on macOS at
https://forums.macrumors.com/threads/usb-3-x-pcie-cards-for-classic-mac-pro.1501482/
An ASMedia ASM3242 USB 3.2 gen 2x2 controller is used with a non-Apple driver to do 20 Gbps mode.
I don't know of any other controllers that support gen 2x2.

 

[Significant1]

I agree - I use the earliest spec number for each mode
5 Gbps USB 3.0 (uses 8b/10b -> 4 Gbps)
10 Gbps USB 3.1 gen 2 (uses 128b/132b encoding -> 9.70 Gbps)
10 Gbps USB 3.2 gen 1x2 (uses 8b/10b encoding -> 8 Gbps)
20 Gbps USB 3.2 gen 2x2 (uses 128b/132b encoding -> 19.39 Gbps)

The linked thread has a bunch of examples showing how the M1 Mac USB controller is not as performant as a USB controller ought to be. You can connect other USB controllers via Thunderbolt to get most of the performance back.

Read about 3.2 gen 2x2 testing on macOS at
https://forums.macrumors.com/threads/usb-3-x-pcie-cards-for-classic-mac-pro.1501482/
An ASMedia ASM3242 USB 3.2 gen 2x2 controller is used with a non-Apple driver to do 20 Gbps mode.
I don't know of any other controllers that support gen 2x2.

Google spying on my activity suggested this youtube video about the subject:

The gist is, that one thing is synthetic benchmark apps, another is real life usage apps. For his usecase testing there was no significant difference in speed depending on how he connected, even compared to internal ssd.

 

[hakr100]

I suspect the lack of speed I expected with my T7 is sort of a non-issue with me, beyond the annoyance of not getting what I expected. I use the T7 to offload photos, music, commercial movies and videos, et cetera, and I am sure they will load and allow editing at more than adequate speeds. I'm certainly not going to spend a couple of hundred bucks on a Thunderdud hub so the T7 will run a bit faster. At home, I can reach my printers via wi-fi and if I need to plug into my router, I have a dongle for that. It's just a disappointment that the T7 runs slower on my new MBA than it does on my iMac.

 

[Fomalhaut]

I have a new MBA M1 and a new Samsung SSD Model T7. Almost nothing on either drive. External SSD is plugged directly into the MBA. I am getting 650 MB/s on writes with the Samsung and 694 MB/s with reads.

I then plugged the Samsung T7 into my 2020 iMac and got 900 MB/s writes and 916 MB/s reads, significantly faster - about one-third faster -than the same drive on my new MacBook Air.

Both tests with the cable supplied by Samsung. The internal and portable drives are formatted APFS. Tests run with the Black Magic Disk Speed Test.

Any ideas why the Samsung drive is about one third faster when plugged into the iMac?

Have you read through this thread? https://forums.macrumors.com/thread...ally-10gb-s-also-definitely-not-usb4.2269777/

Most people (myself included) are seeing significantly slower throughput from external USB drives on M1 Macs. In my case, my 10Gbps drive only connects at 5Gbps on the M1 Mini, but at 10Gbps on my MBP16.

As you've seen, even if it connects at 10Gbps, which I assume yours does given the speeds you reported, it is a lot slower than on a modern Intel Mac. Whether Apple can fix this with a software or firmware upgrade remains to be seen.

 

[Fomalhaut]

If I am not mistaken, it is because your drive support usb 3.2 10gbps, while m1 is usb 4 and usb 4 does not support 3.2 10gbps. USB 4 does have a 10gbps mode, but it is not electrical compatible with 3.2gbps. the work-around is a thunderbolt dock with usb 3.2 10gbps support, else you are connected at "only" 5gbps.

USB4 - Wikipedia

en.wikipedia.org

If the OP is getting >650MBps they must be connected at greater than 5Gbps. Even without 8b/10b encoding (requiring 10 bits for every byte), it would be a maximum of 625MBps, and AFAIK real world USB 3.1 is more likely to top out at about 480MBps.

There is clearly an issue with the M1 USB controllers not matching the same performance as recent Intel Macs supporting USB 3.1Gen2 or 3.2Gen2x1.

 

[Significant1]

If the OP is getting >650MBps they must be connected at greater than 5Gbps. Even without 8b/10b encoding (requiring 10 bits for every byte), it would be a maximum of 625MBps, and AFAIK real world USB 3.1 is more likely to top out at about 480MBps.

There is clearly an issue with the M1 USB controllers not matching the same performance as recent Intel Macs supporting USB 3.1Gen2 or 3.2Gen2x1.

Yeah, in my mind we where talking about just below 400MB/s. Don't know from where and how I mixed that up. YouTube, Reddit another thread here on macrumors ¯\_(ツ)_/¯

Anyway it not a real concern for me, 650MB/s is plenty for me and Apple only promise up to 10gbps. But, if I had bought a mini with 256GB with the intention to use a usb-dock/drive as permanent drive and working with lots of big files, I might have been a bit more anoyed.

 

[gogogo2]

Update to thunderbolt 3 ssd, you get 2000m/s

 

[hakr100]

If the OP is getting >650MBps they must be connected at greater than 5Gbps. Even without 8b/10b encoding (requiring 10 bits for every byte), it would be a maximum of 625MBps, and AFAIK real world USB 3.1 is more likely to top out at about 480MBps.

There is clearly an issue with the M1 USB controllers not matching the same performance as recent Intel Macs supporting USB 3.1Gen2 or 3.2Gen2x1.

That seems like the logical answer. I'm not technically equipped to comment further, and can only offer my observations. But your answer is the same one, basically, that Samsung gave me.

 

[Fomalhaut]

Update to thunderbolt 3 ssd, you get 2000m/s

Yes indeed, but for extra $$$ ! One of the inconveniences is that there are only a couple of external SSDs or enclosures that can do both TB3 and USB (Acasis USB4/TB3 enclosure and an SSD from Sabrent).

The fastest options seem to require NVMe with PCIe 4.0 SSDs which are still really expensive.

 

[jkarol3]

I have a new MBA M1 and a new Samsung SSD Model T7. Almost nothing on either drive. External SSD is plugged directly into the MBA. I am getting 650 MB/s on writes with the Samsung and 694 MB/s with reads.

I then plugged the Samsung T7 into my 2020 iMac and got 900 MB/s writes and 916 MB/s reads, significantly faster - about one-third faster -than the same drive on my new MacBook Air.

Both tests with the cable supplied by Samsung. The internal and portable drives are formatted APFS. Tests run with the Black Magic Disk Speed Test.

Any ideas why the Samsung drive is about one third faster when plugged into the iMac?

This is now a known issue on all Mac M1 units. I have the same issue as you did. No issue using a TB drive but the others are slower vs intel macs. here is the reason:

M1 Mac: USB only 5 Gbit/s instead of 10 Gbit/s ⌚️ 🖥 📱 mac&egg

It seems that external SSDs on an M1 only work with one USB lane, which limits the throughput to 5 Gbit/s.

macandegg.com

 

[Fomalhaut]

I have a new MBA M1 and a new Samsung SSD Model T7. Almost nothing on either drive. External SSD is plugged directly into the MBA. I am getting 650 MB/s on writes with the Samsung and 694 MB/s with reads.

I then plugged the Samsung T7 into my 2020 iMac and got 900 MB/s writes and 916 MB/s reads, significantly faster - about one-third faster -than the same drive on my new MacBook Air.

Both tests with the cable supplied by Samsung. The internal and portable drives are formatted APFS. Tests run with the Black Magic Disk Speed Test.

Any ideas why the Samsung drive is about one third faster when plugged into the iMac?

[Edit: oops...just realized this is an old thread that I've already answered...oh well...here's a repeat of my previous answers]

There is a whole thread on just this subject..

The consensus is that the USB 3.1 interface implementation on the M1 Macs is slower than Intel Macs. It may be drivers, it may be hardware, it may be some other limitation of the M1.

The problem also manifests itself with difference USB link connection speeds with different enclosures. Some USB 3.1Gen2 enclosures, which should support 10Gbps links, only connect at 5Gbps (USB 3 / 3.1gen1).

I have Samsung T5 and T7 drives (and a load of other externals) and have the same results.

You can get slightly better performance plugging the drive via USB-C into a Thunderbolt 3 dock. The connection to the Mac is then via Thunderbolt. I get about 750/840MB/s (read/write) on my T7 when going via CalDigit TB3 dock. Writes are consistently faster than reads.

 

[Fomalhaut]

If I am not mistaken, it is because your drive support usb 3.2 10gbps, while m1 is usb 4 and usb 4 does not support 3.2 10gbps. USB 4 does have a 10gbps mode, but it is not electrical compatible with 3.2gbps. the work-around is a thunderbolt dock with usb 3.2 10gbps support, else you are connected at "only" 5gbps.

USB4 - Wikipedia

en.wikipedia.org

The T7 connects to my M1 Mini at 10Gbps, but is still slower than when connected to an Intel Mac. It is not just a question of USB 3.1gen2 / 3.2 compatibility.

You wouldn't be able to get almost 700MB/s via a 5Gbps connection. When connected via the 5Gbps USB-C on my Calidigit dock, the results are far slower:

There is something amiss with M1 USB interface hardware or drivers.

 

[joevt]

The T7 connects to my M1 Mini at 10Gbps, but is still slower than when connected to an Intel Mac. It is not just a question of USB 3.1gen2 / 3.2 compatibility.

You wouldn't be able to get almost 700MB/s via a 5Gbps connection. When connected via the 5Gbps USB-C on my Calidigit dock, the results are far slower:
View attachment 1805912

There is something amiss with M1 USB interface hardware or drivers.

Correct. The M1 connects at 10 Gbps or 5 Gbps, but it transfers USB packets less efficiently (larger spaces between packets or smaller packets?) so it's slower than Intel Macs whether you're doing 10 Gbps or 5 Gbps. I haven't seen tests for 480 Mb/s but I don't think anyone cares about speed for USB 2.0 devices.
There are some cases with the M1 Macs where a 10 Gbps device connects at only 5 Gbps - that's a separate issue.

USB on M1 Macs isn't actually 10Gb/s? (Also definitely not USB4)

After quite a bit of testing, I have concluded that the USB bus on at least my Mac mini M1 does not actually support "USB 3.1 Gen 2 (up to 10Gb/s)" as listed on the Tech Specs page. I have a Samsung T5 USB-C SSD. It supports "USB 3.1 Gen 2 10Gb/s" (Gawd, I hate USB 3.1+ naming conventions...†)...

forums.macrumors.com

 

[joevt]

This is now a known issue on all Mac M1 units. I have the same issue as you did. No issue using a TB drive but the others are slower vs intel macs. here is the reason:

M1 Mac: USB only 5 Gbit/s instead of 10 Gbit/s ⌚️ 🖥 📱 mac&egg

It seems that external SSDs on an M1 only work with one USB lane, which limits the throughput to 5 Gbit/s.

macandegg.com

That article is mistaken about the problem. The Samsung T5 is one lane - the product page says it is USB 3.1 gen 2. Gen 1x2 and Gen 2x2 are options for USB 3.2 (not USB 3.1). The reason the T5 runs at 5 Gbps is not because it is switching from Gen 1x2 to Gen 1x1, it is because it is switching from Gen 2x1 to Gen 1x1.

macOS doesn't support two lane USB 3.2. No Macs have two lane USB 3.2. To use two lane USB, you need a PCIe card with USB-C Gen 2x2 USB controller and a driver (I have one but haven't tried it yet - one person did try it successfully with a third party open source driver).

Although Gen 2x1 and Gen 1x2 are both 10 Gbps, Gen 2x1 is faster because it uses 128b/132b encoding (9.7 Gbps). Gen 1x2 uses 8b/10b encoding (8 Gbps).