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Comment by PragmaticPulp | Hacker News Reader

I understand why the Raspberry Pi uses SD cards (cost, simplicity, ease of use) but the entire line would be so much more useful with onboard eMMC storage.

SD cards are great for keeping cost down and getting started quickly by flashing OS images from a PC. However, enthusiasts spend so much time fiddling with external storage options and cobbling together messes of powered USB hubs, cables, external enclosures, and fiddling with kernel issues (USB attached SCSI) that a Raspberry Pi with built-in eMMC would be a breath of fresh air.

They could even keep costs down by adding a connector for an eMMC submodule, similar to what ODROID has done with their boards.

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Personally I wish they'd add an m2 slot and scrap the SD card. It really is the bottleneck of the whole system.

But they walk a fine balance with PCB space, backward compatibility, performance, cost and user-friendliness.

The speed would be much better than an SD card, but nowhere near the peak M.2 performance we've come to love. The SoC they use only has a single lane of PCIe Gen 2. So 500 MB/s peak (MB, not MiB) with large transfers.

Throw in a PCIe switch or something so you can still attach a USB 3 controller and now you've doubled the price and power consumption.

What's really hindering responsiveness and day-to-day performance isn't going to be sequential read and write speeds but rather 4K random IOPS.

SD cards are not all designed or optimized around small, random reads and writes - the typical workload of a boot drive - and latencies can be staggering. Similar for USB sticks. On the other hand, these days the overwhelming majority of M.2 SSDs are at least somewhat optimized for 4K IOPS. The latest Sabrent Rocket M2 SSDs get some 650,000 4K IOPS vs eMMC at ~13000 (the Rocket is 50X faster) an SD card around ~2000 (the Rocket is 325X faster).

Frankly if you stuck a Sabrent Rocket on a PCIe 1.0 x1 connector the performance would absolute savage an SD or eMMC solution on this workload. Even if they somehow also had identical sequential I/O specs.

If they add a m.2 slot now, at least it's already there for the next revision which they could improve the PCIe lane.

And hopefully that would ensure the new form factor to be somewhat stable for a while after that.

They could add a SATA M.2 slot, then it's equivalent to using a 2.5" SATA SSD but in a neater form factor.

500MBPS is already 1.5x SSD speed, so... I'd take it over SD any day of the week! Especially since at those speeds, you can buy just any random cheap m.2 and come out well on top.

500 MB/s is more than enough for most applications.

m.2 slot is definitely the best long term issue for keeping costs down but providing a way for high speed. Now that they’ve switched to USB, I don’t see power draw as an issue any longer.

It depends what you want to do with it. If you want to use it for a mobile robot, run the Raspberry Pi off a battery, then yes, power does matter.

I suspect the power draw of a mobile robot would be dominated by the motors, would it not?

The motors aren't necessarily constantly on, and you don't need very big motors for a small robot.

Ack, why do away with SD slot? Sure add an nvme port that would be awesome but don't take away stuff, that's why we lost aux out on phones!

USB SD card readers are cheap, if you need one. Many hubs have one built in anyway.

SD card reading on the chip is also cheap, and doesn't require removing if you add an m.2 connector. No need to get rid of SD.

It might require removing to save on the physical space - an m2 connector requires a large amount of physical space compared to the SD card (for the retention screw). It might not have room for both.

So... that's fine, then? Telling people "you get an SD card connector and an m.2, you can't use both at the same time" seems perfectly reasonable to me. Have them overlap, done. Now people who want to use a $5 SD card with the slow speeds that come with that can do so, and people who want high speed but with the higher cost of a reliable m.2 drive instead can do so, too. No one loses.

yes but an sd card can be bought for less than 10 $/€, whereas an nvme disk would cost about the same price of the whole rpi.

you have to keep in mind the original goal of the raspberry pi project.

if you want nice performance and low power consumption, you're better off considering a cheap intel nuc.

SSD: $20 for 128GB on Amazon

SD card: $15.20 for 128GB on Amazon

The price difference is minimal.

But the SSD is much much faster in that price range.

You're missing one of the very important aspects of a RPI is that it's cheap and accessible. Many countries around the world, particularly the poorer ones, don't have Amazon or ready cheap access to SSDs. What they do have access to is phone micro SD cards in adaptors. An 8 or 16GB card is plenty for a computer lab and is affordable and accessible.

Which country doesn't have access to SSDs?

They are saying that having an SD port allows people to spend less by using 8-16gb storage cards that are much cheaper than a 128gb M2 SSD. In many countries the RPi is already a big expense on itself and import taxes and low demand often inflate its price even higher. Same happens to other electronics, combined with the reduce buying power, it all adds up really quick.

Last time I checked, a NUC was considerably more expensive..

The default intent, and thus the default configuration, is to have a device that a kid can accidentally nuke without any lasting consequences. That's the whole founding principle of the thing. Lose that and you've lost the Raspberry Pi as a concept.

> is to have a device that a kid can accidentally nuke

To be honest the large majority of RPi users I have ever met are only adults. Are there a lot of kids who are using it out there?

We would like the RPi more for education, but the cost is still a factor. Due to cost, the school need to buy these, as by itself the RPi is useless; It needed a keyboard, mouse, screen, etc.

Students bring their own SD card, since else they are easily misplaced (stolen). This also means boards can be used by any student.

A lot of effort and cost, so we went with the microbit. The kids can easily own them, use a tablet to program them, and for the kids that are older, they can go for the rPi to expand this setup and learn more advanced stuff. By we do not use this as an entry. Kids that do robotics have a better time with them.

So yes, maybe mostly used by adults. The idea of SD cards was a good one. But several flaws held it back; like the non-5v tolerant GPIO. Lost several boards due to misuse... And they ain't cheap if they need to be replaced often.

Actually, yes. They're even good in a classroom because even if a kid screws one up, it's not hard to teach a public school teacher how to re-image an SD card.

You dont hear about it as often because for reasons, the kids aren't exactly encouraged to reach out to adults on the internet. Dogs on the internet and all that.

You sir, must have never played the IT guy to this teacher you speak of in our public school system. I challenge the “easy” assertion with great confidence.

/meant humorously but also seriously serious.

Do adults meet a lot of kids without adults present though? This seems like a bit of observer bias.

Yep. Kids don't tend to blog. Maybe brag, but still in a different scenario ;-)

eMMC isn't mutually exclusive with having an SD card slot.

Even if they removed the SD slot, you would still reflash the board over USB. That's how it's done with the Raspberry Pi Compute Module. With some software development it could be even easier than fiddling with SD cards.

In education environments, microSD cards tend to disappear a lot. Having one less moving piece to lose would be a win.

And having flashed cards ready to hand over is a win. "Factory reset" in the time it takes to swap a card. Your point? The Pi (apart from the CM) is for kids. It happens to be useful to other people as well, but that is not, was not, and never will be the aim of the Foundation.

It is when they have to build the thing for <$25 though.

Misplaced cards happen, but it does allow easier sharing of the boards.

PinePhone even has a great solution for the eMMC ease of use problem. The bootloader loads from eMMC by default (and I believe comes preloaded with a distro based on what version you bought) unless there is a bootable (micro)SD card inserted. There's a popular bootable SD card image for the PinePhone that exposes the eMMC over USB allowing flashing using `dd` or similar, which makes the whole process rather painless compared to the mess that is raspberry pi.

I agree. I have run quite a few Raspberry Pi over the years and so many of them died because of SD card corruption. Eventually I got a NanoPC T4 with built in eMMC and it’s been tugging along for a good 2 years with zero issues.

I've never experienced this SD card corruption, even when power goes down to the Pi. I believe it happens, but I wonder what my unique circumstances are. Is it that I always use Samsung or SanDisk SD cards with the Pi?

> Is it that I always use Samsung or SanDisk SD cards with the Pi?

Quite possibly! Flash memory is absolutely not all the same. I wish someone would do for SD cards what Backblaze does for hard drives.

> Is it that I always use Samsung or SanDisk SD cards with the Pi?

Oddly enough, Samsung, SanDisk, and Sony are the three brands I've had die on me. I had a GoPro eat two Sony cards in less than a year, I switched to SanDisk Endurance and it's been plugging along for about 2 years now. I've had one Samsung and a couple SanDisk SD cards die in Raspberry Pi's. I'm currently using MicroCenter, AData and one other lower tier brand that have held up much better than the name brands.

Those will still eventually die due to log being written to the card using all available read/write cycles.

You mean /var/log or filesystem log? What about using non-journaling filesystems or keeping /var/log on a ramdisk?

That's a problem that will eventually affect any flash solution -- SD card, SSD, or USB flash.

They usually just stop accepting writes (silently). It's a bit of a head scratcher at first. But at least it doesn't lead to a complete data loss.

> I have run quite a few Raspberry Pi over the years and so many of them died because of SD card corruption

The Pi themselves don't die because of a SD corruption. Only the SD cards do (and they can be recovered).

I've had a raspberry with SD card for more than 3 years now, still working fine. YMMV obviously

Had similar and switched to a cheap used desktop. I was running Home Assistant [1] and my guess is the constant writing of state history into the database slowly killed the card.

[1]: https://www.home-assistant.io/

I browsed the datasheet [1] for the BCM2711 processor and did not see an eMMC controller on this part. Assuming the SD card is connected by SPI which would explain why it's so slow. Also rules out eMMC.

[1] https://datasheets.raspberrypi.org/bcm2711/bcm2711-periphera...

The Raspberry Pi Compute Module 4 has eMMC.

Jeff Geerling benchmarked it and found it faster than his fastest SD card: https://www.jeffgeerling.com/blog/2020/raspberry-pi-compute-...

It's definitely not NVMe fast, but it's perfect for average workloads.

Weird. So the processor has an eMMC controller but they left that out on the datasheet.

The publicly-available datasheets for the SoC in the Pi are incredibly, and as far as I can tell intentionally, incomplete. The SD card controller is just one of the things lacking public documentaiton.

The physical layer for eMMC is SDIO- the same is used for SD cards, at least if you want more than ~ a megabyte/s of interface bandwidth.

IIRC the layers above SDIO are slightly different for eMMC and SD(HC), but generally SoCs that have SDIO interface support both types of memory.

For those who don't know eMMC is basically an SD card that is soldered to the board

eMMC has several advantages over microSD cards.

For example, the microSD slot only has 4 data lines. eMMC isn't constrained to the microSD slot, so they can have 8 data lines.

The Raspberry Pi 4 Compute Module has onboard eMMC. Jeff Geerling tests a lot of SD cards on the Raspberry Pi, but he found the CM4's eMMC is faster than any SD card he's ever tested: https://www.jeffgeerling.com/blog/2020/raspberry-pi-compute-...

Then do we have "eMMC" equivalent quality SD cards that lasts just as long?

Yes, they're marketed as "industrial grade MicroSD cards" and are available via electronics component distributors like Digi-Key.

e.g. https://www.digikey.com/en/products/detail/swissbit/SFSD032G...

That costs more than the rpi itself!

is there anything marketed as "industrial grade X" that costs less than a rpi?

Drop the e and you have an MMC card.

Why is that more useful than a removable SD card?

I think the comment was a bit tongue-in-cheek. The underlying storage tech between is the same, but eMMCs have a controller that handles the actual layout of the data. In a removable SD card setup, this is handled by the CPU, which of course has many other things to worry about. Having its own controller makes eMMCs more reliable.

"eMMCs have a controller that handles the actual layout of the data"

Maybe there is some part that eMMCs have that SD cards don't, but SD cards absolutely do have a controller that does layout (wear levelling). It doesn't do the filesystem layer, but IIRC eMMC's don't either.

AFAIK the only reason SDs are less reliable, is because they're cheap and the socket can be loose, causing corruption during a write (or wear level). It would be interesting if you know of something logically different that also makes them less reliable.

SD cards used to be optimized for usage patterns typical in a video or foto camera (big files, written at once). eMMCs are better adapted to serve as a traditional filesystems for e.g. phones.

Don't find source now though, so maybe I'm completely wrong.

That's true, I remember reading that somewhere too.

The main advantage of eMMCs in reliability is that you can't buy a RPi with a eMMC for camera use soldered on. You can have this same advantage by buying the right kind of SD cards (embdedded/industrial ones, or on a budget, overkill capacity "surveillance" camera cards that advertise wear leveling).

3B+ forward has support for USB boot, as of I think July this year it was built into the firmware for the 4b. I have a Zw with SD card as it requires more or less but everything lese is USB based with drives I swap around for raspbian, ubuntu, retropi/etc. But setting that up does require an SD card with respbian unless the pi shipped with the newest firmware.

I'm not against on board storage but I understand the tradeoff to allow user expandability and reduce production costs. I think they'd get heat on the eMMC size unless it was like 32gb and I don't think that cost increase would make it very far. But maybe with the push to the 400 they will start to go that route to create a self contained but expandable system that is plug and play raspbian by default.

I think the key advantage of SD cards is they're easy to understand and use (once flashed). Conceptually it's simple to explain that the software lives on that little card. Want to change the OS? Swap the card. Plus it makes it easy for people who aren't comfortable flashing to buy a card with their OS of choice installed and ready to go.

The Raspberry Pi 4 Compute Module has eMMC

Yes, I gave up on my rasp pi because of the instability of sd cards. It could barely run a few weeks without manual intervention. Honestly I have no clue how anyone does anything useful with them. Tried using usb attached ssd for a while, but never got it so stable that a remote reboot (or power loss) had acceptable risk.

I hear that many people are plagued with SD card issues. But I’m running probably ten raspberry pi’s right now and while I’ve had a couple SD card issues over the years, that has seemed to be the exception rather than the rule.

Yeah, well when running remotely it must come back by itself every single time, and I was unable to get reliable results over 6 months of testing. It might 3 months until I can travel and replace a nonbooting instance, and I will not even know what is wrong!

SD cards are getting nvme in the future with 7.0 specification. I wonder how that will affect performance.

https://www.slrlounge.com/sd-express-memory-cards-pcle-nvme/

They could implement UFS 2 if they wanted higher speed.

But cost is supreme in the case of the pi.

It's sort of like Elon Musk saying on Electric Vehicles: "We could make the car infinitely desirable, but if someone does not have the money, they won't buy it"

Just pull up https://www.raspberrypi.org and you'll immediately see "someone" is kids.

So I think the fiddling is a given, maybe part of the experience, and usually there's a payoff.

that said I'm not immune to wishful thinking. I think an expensive $150 Pi Pro that makes a profit would be cool. Think mini-itx, pcie, m.2 and memory slots PLUS gpios.

It would be better if it had a built in fast flash of about 8GB. That’s enough to run the OS and do basics and if you want more, add it via one of the external ports.

> and fiddling with kernel issues (USB attached SCSI)

That's actually a good thing, the raspberry pi community uncovered a ton of issues over the years related to storage drives over USB, which has been or can now be patched in the kernel to make such things more reliable.

The eMMC submodule works just as well as a SD card when writing it on another system, the submodule plugs into a small PCB with SD card traces on one end, you then plug the whole lot into a SD card slot.

I disagree. When your eMMC degrades, your Pi turns into e-waste. With SD cards you get to enjoy the progress. In both speed and price per GB.

Why would you want eMMC? I'd rather not have to deal with broken eMMC. And non-upgradeable storage.

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