iurly
Posts: 23
Joined: Sun May 14, 2017 10:50 pm

HAT for storage (e.MMC?)

Fri Jan 17, 2020 4:10 pm

Hi,

I've been looking for a way to add some long-endurance storage (in the range of 64-128GB) to a Raspberry Pi 3 for data logging applications.
So far I've been using an USB-SATA adapter with an external SATA SSD, but this has been creating more problems than it has solved, namely due to excessive power consumption on the USB port.
USB Flash Drives, which I've used in the past, have proven extremely unreliable in the long run.
[BTW, I believe USB does not seem to lend itself to industrial-like applications].

So I was thinking of maybe a HAT with an embedded e.MMC, but I could not find anything.
If I were to make a custom HAT and put an e.MMC on it, would there be a way for the Raspberry Pi to access it, while keeping the OS on the microSD? I believe the RPI3 has a single SD/eMMC interface and it's currently used for the microSD slot.

Otherwise, wouldn't just a properly-sized industrial microSD XC do the job?
An industrial-grade 64GB SDXC with underlying MLC flash should cost around 80$, which is a lot but not so much after all.
What would be the disadvantages compared to an equivalent eMMC?

Any other suggestions?

Thanks!

trejan
Posts: 1217
Joined: Tue Jul 02, 2019 2:28 pm

Re: HAT for storage (e.MMC?)

Fri Jan 17, 2020 4:42 pm

iurly wrote:
Fri Jan 17, 2020 4:10 pm
If I were to make a custom HAT and put an e.MMC on it, would there be a way for the Raspberry Pi to access it, while keeping the OS on the microSD? I believe the RPI3 has a single SD/eMMC interface and it's currently used for the microSD slot.
Pi 0-3 has two SD controllers. One is SD only and is for the SD slot whilst the other is a SDHCI SD/SDIO controller so it is used for onboard WiFi. If you disabled the onboard WiFi then you could set the pinmux to have the SDHCI controller on the GPIO header.

Pi 4 has three SD controllers. The old SD slot controller is now spare as they added a new faster one for the SD slot.

Your existing solution with a USB attached SSD will be greatly faster so if high throughput is essential then you'll have to keep using the USB setup.

iurly
Posts: 23
Joined: Sun May 14, 2017 10:50 pm

Re: HAT for storage (e.MMC?)

Fri Jan 17, 2020 5:01 pm

I see, thanks for the heads up!
High throughput is not a requirement but reliability is.
Any suggestion for some robust solution with USB storage? An external SSD with USB adapter also poses mechanical issues.

Otherwise, just using the microSD?
Thanks!

hippy
Posts: 6859
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: HAT for storage (e.MMC?)

Fri Jan 17, 2020 7:16 pm

iurly wrote:
Fri Jan 17, 2020 5:01 pm
High throughput is not a requirement but reliability is.
What actual throughput do you want or need ?

It should be possible to add Eeprom, MMC or SD Card on a home made add-on 'HAT' and bit-bang it I don't know much about eMMC but would have thought that would equally be possible.

drgeoff
Posts: 10356
Joined: Wed Jan 25, 2012 6:39 pm

Re: HAT for storage (e.MMC?)

Fri Jan 17, 2020 11:08 pm

Is there any evidence that eMMC is more reliable or has better long term endurance than SD or USB flash drive?

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