IoT2018
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Connecting M.2 Module to Raspberry Pi

Thu Jun 21, 2018 10:44 pm

Hi,

I have a module that uses M.2 slot to communicate with my laptop. The module is used for extremely high data transfer and it achieves around 2 Gbps over the air.

So my question, is there any extension board for Raspberry Pi to connect this module with M.2 connector?

There is an extension board to convert M.2 SATA to USB 2. But this extension does not work in my case, since my module has a different type of connector.
https://www.startech.com/eu/HDD/Adapter ... pi~PIB2M21

Thanks.

ghans
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Re: Connecting M.2 Module to Raspberry Pi

Fri Jun 22, 2018 5:15 am

Th Raspberry Pi does not support PCI, SATA or USB 3 (USB 2 works). Which bus is being used internally by your M.2- sized module ? No PCI device will ever properly work with any existing Raspberry Pi.

ghans
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W. H. Heydt
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Re: Connecting M.2 Module to Raspberry Pi

Fri Jun 22, 2018 5:42 am

You would have to find hardware that would convert PCI to USB 2. Good luck, you'll need it.

There is no actual point (other than size) to try to use an M.2 module with a Pi. You're going to be limited to USB 2 speed: 480Mb/s no matter what you do. The same applies to SATA SSD, too, but a case can be made for SSD over HDD in that SSD has no moving parts. Even if a future Pi has USB 3, you still wouldn't get full benefit from a SATA III device.

IoT2018
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Re: Connecting M.2 Module to Raspberry Pi

Fri Jun 22, 2018 10:51 am

ghans wrote:
Fri Jun 22, 2018 5:15 am
Th Raspberry Pi does not support PCI, SATA or USB 3 (USB 2 works). Which bus is being used internally by your M.2- sized module ? No PCI device will ever properly work with any existing Raspberry Pi.

ghans
Thanks for the reply. My M.2 Size module uses PCI as I can see the module when I execute in lspci command in Linux.

IoT2018
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Re: Connecting M.2 Module to Raspberry Pi

Fri Jun 22, 2018 10:53 am

W. H. Heydt wrote:
Fri Jun 22, 2018 5:42 am
You would have to find hardware that would convert PCI to USB 2. Good luck, you'll need it.

There is no actual point (other than size) to try to use an M.2 module with a Pi. You're going to be limited to USB 2 speed: 480Mb/s no matter what you do. The same applies to SATA SSD, too, but a case can be made for SSD over HDD in that SSD has no moving parts. Even if a future Pi has USB 3, you still wouldn't get full benefit from a SATA III device.
Thanks for the answer. The module that I want to connect comes only with M.2 connector but with USB 2 I am very limited in terms of speed.

W. H. Heydt
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Re: Connecting M.2 Module to Raspberry Pi

Fri Jun 22, 2018 6:43 pm

IoT2018 wrote:
Fri Jun 22, 2018 10:53 am
W. H. Heydt wrote:
Fri Jun 22, 2018 5:42 am
You would have to find hardware that would convert PCI to USB 2. Good luck, you'll need it.

There is no actual point (other than size) to try to use an M.2 module with a Pi. You're going to be limited to USB 2 speed: 480Mb/s no matter what you do. The same applies to SATA SSD, too, but a case can be made for SSD over HDD in that SSD has no moving parts. Even if a future Pi has USB 3, you still wouldn't get full benefit from a SATA III device.
Thanks for the answer. The module that I want to connect comes only with M.2 connector but with USB 2 I am very limited in terms of speed.
That's pretty much the point of the M.2 standard. Your module probably also uses NVME protocol, as well. And, yes, USB 2 is a pretty severe speed limitation for mass storage. My testing indicate that one can expect transfer rates around 25MB/s to nearly 35MB/s, but that's about it. Many SATA III SSDs can hit 500+ MB/s transfer rates...if what they're attached to can handle it. An NVME PCI solid state device could do as much as 2.5GB/s given the proper interface.

This whole issue is why I am hoping that a future Pi--possibly as early as the "Pi4B" in a year or two--will include a USB 3 interface. That would potentially push actual transfer rates into the 300+MB/s rate, which would probably exceed nearly any HDD and make inexpensive SSDs run close their actual limits. Until that happens, though, the case for an M.2 device or even an SSD is rather limited.

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HawaiianPi
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Re: Connecting M.2 Module to Raspberry Pi

Fri Jun 22, 2018 8:08 pm

W. H. Heydt wrote:
Fri Jun 22, 2018 6:43 pm
That's pretty much the point of the M.2 standard. Your module probably also uses NVME protocol, as well. And, yes, USB 2 is a pretty severe speed limitation for mass storage. My testing indicate that one can expect transfer rates around 25MB/s to nearly 35MB/s, but that's about it.
I've gotten 40MB/s with SSD.

Many SATA III SSDs can hit 500+ MB/s transfer rates...if what they're attached to can handle it. An NVME PCI solid state device could do as much as 2.5GB/s given the proper interface.
Fastest I've seen from a SATA3 SSD is around 560MB/s from a Crucial MX500, but the Samsung 960 Pro NVMe SSD does quite a bit better than 2.5GB/s in my Lenovo Y520 budget gaming laptop (that drive is a beast).
SS960Pro512GBNVMe.jpg
SS960Pro512GBNVMe.jpg (51.04 KiB) Viewed 929 times

This whole issue is why I am hoping that a future Pi--possibly as early as the "Pi4B" in a year or two--will include a USB 3 interface. That would potentially push actual transfer rates into the 300+MB/s rate, which would probably exceed nearly any HDD and make inexpensive SSDs run close their actual limits. Until that happens, though, the case for an M.2 device or even an SSD is rather limited.
The main advantage of SSD on a Pi is higher IOPS and better random I/O performance. Raw throughput won't be much better than a very fast SD card (limited by USB 2.0), but reduced latency and better random I/O performance makes the system feel faster. Admittedly the difference isn't huge. Certainly nowhere near the difference you feel on a more mainstream PC when switching from HDD to SSD, but it is noticeable.

SATA3 SSD on USB 3.0 tops out at just under 5GB/s (a little slower than native SATA3). There would be literally no point to an M.2 NVMe to USB adapter, as it would offer no performance advantage.
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W. H. Heydt
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Re: Connecting M.2 Module to Raspberry Pi

Fri Jun 22, 2018 9:45 pm

HawaiianPi wrote:
Fri Jun 22, 2018 8:08 pm
W. H. Heydt wrote:
Fri Jun 22, 2018 6:43 pm
Many SATA III SSDs can hit 500+ MB/s transfer rates...if what they're attached to can handle it. An NVME PCI solid state device could do as much as 2.5GB/s given the proper interface.
Fastest I've seen from a SATA3 SSD is around 560MB/s from a Crucial MX500, but the Samsung 960 Pro NVMe SSD does quite a bit better than 2.5GB/s in my Lenovo Y520 budget gaming laptop (that drive is a beast).
I wasn't hunting for exact figures. 560MB/s is "500+MB/s".
This whole issue is why I am hoping that a future Pi--possibly as early as the "Pi4B" in a year or two--will include a USB 3 interface. That would potentially push actual transfer rates into the 300+MB/s rate, which would probably exceed nearly any HDD and make inexpensive SSDs run close their actual limits. Until that happens, though, the case for an M.2 device or even an SSD is rather limited.
The main advantage of SSD on a Pi is higher IOPS and better random I/O performance. Raw throughput won't be much better than a very fast SD card (limited by USB 2.0), but reduced latency and better random I/O performance makes the system feel faster. Admittedly the difference isn't huge. Certainly nowhere near the difference you feel on a more mainstream PC when switching from HDD to SSD, but it is noticeable.

SATA3 SSD on USB 3.0 tops out at just under 5GB/s (a little slower than native SATA3). There would be literally no point to an M.2 NVMe to USB adapter, as it would offer no performance advantage.
[/quote]
Careful... SATA III is 6Gb/s. USB 3 is 5Gb/s, or--theoretically, if you ignore overhead--a bit over 800MB/s. To get 5GB/s you'd need an interface that runs at the better part of 50Gb/s and no USB standard comes anywhere near that.

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HawaiianPi
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Re: Connecting M.2 Module to Raspberry Pi

Sun Jun 24, 2018 8:36 pm

W. H. Heydt wrote:
Fri Jun 22, 2018 9:45 pm
I wasn't hunting for exact figures. 560MB/s is "500+MB/s".
Yes, of course, and I was just commenting on how ridiculously fast the Samsung EVO 860 Pro NVMe drive is.

...the case for an M.2 device or even an SSD is rather limited.
Certainly in smaller sizes a strong case can be made for micro SD cards (I own several A1 rated 32 & 64 GB cards myself), but in sizes from 128GB up, an SSD can cost less than an A1 rated micro SD card, so for people with larger storage needs it is a practical solution, even if it's not going to be orders of magnitude faster.

Careful... SATA III is 6Gb/s. USB 3 is 5Gb/s, or--theoretically, if you ignore overhead--a bit over 800MB/s. To get 5GB/s you'd need an interface that runs at the better part of 50Gb/s and no USB standard comes anywhere near that.
Whoops, I meant 5 giga bits per second, not giga-bytes. Sorry about that. :oops:
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Re: Connecting M.2 Module to Raspberry Pi

Sun Jun 24, 2018 11:25 pm

HawaiianPi wrote:
Sun Jun 24, 2018 8:36 pm
W. H. Heydt wrote:
Fri Jun 22, 2018 9:45 pm
...the case for an M.2 device or even an SSD is rather limited.
Certainly in smaller sizes a strong case can be made for micro SD cards (I own several A1 rated 32 & 64 GB cards myself), but in sizes from 128GB up, an SSD can cost less than an A1 rated micro SD card, so for people with larger storage needs it is a practical solution, even if it's not going to be orders of magnitude faster.
I quite agree that when larger storage is used, the case for an SSD or HDD is strong. I put the threshold of when to shift from microSD to SSD even lower than you do, as I have Pis with 60GB SSDs. I'm not sure how many Pis (of the 20 million sold) really need more that 16GB, let alone more than 128GB. Especially considering that the CM and CM3 only come with 4GB of eMMC. For a number of my uses, the "sweet spot" is 8GB...enough to hold everything I need without having a lot of space that will never be used. It is getting harder and harder to *find* decent 8GB cards, though, and I can't say that I've seen one that is A1 rated.
Careful... SATA III is 6Gb/s. USB 3 is 5Gb/s, or--theoretically, if you ignore overhead--a bit over 800MB/s. To get 5GB/s you'd need an interface that runs at the better part of 50Gb/s and no USB standard comes anywhere near that.
Whoops, I meant 5 giga bits per second, not giga-bytes. Sorry about that. :oops:
I figured you did. It's just one of the things I jump on because it is so common and so easy to get wrong and lead people astray.

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