Reverse-engineering and analysis of SanDisk High Endurance microSDXC card (2020)

I don't disagree with you, but the other perennial unanswered question on HN is: how do I ensure I'm paying extra for actual quality and not just sucker tax?

Memory cards and ssds are famously obtuse like this. There are the branded versions (custom made for your Switch, for your Xbox,etc) which are exactly the same as their cheaper counterparts. Sandisk itself recently started a "creator" line of cards and ssds which are, again, exactly the same but more expensive. Samsung had Evo Plus which was different than Evo+ but same as Evo Select. Go figure!

Sometimes looking at specs helps but usually not - I.e. The "up to" speed marks are famously irrelevant for real time usage, and brand name companies will offer any number of cards with same specs and tags (u2/v3/class10/mark5/whatever) at varying price points. And then there's the WD Red saga where drives branded "NAS" were completely inappropriate for NAS usage.

I ran a photography business a while back and always bought extreme pro because I just couldn't risk it, but honestly, I felt like a bit of a sucker. It's hard to know when you're actually buying real quality and endurance increase.

Especially with the Raspberry Pi, another point is power delivery. You need a beefy power source, but also a good cable. I bought a USB-C charging cable for my Pi4, and it was very unstable and crashed a lot. Corrupted the install a couple of times, and so I got some new SD cards.

Well, turned out the "charging cable" had 1 ohm resistance and so when the Pi load spiked, the voltages would drop well below 4.5V...

Tossed it away and got a proper cable, and the thing has been rock solid since.

Highly recommend getting a USB cable tester, I had several black sheep in my collection.

Why mount the SD card read/write. Why not mount read-only. After boot, I can remove the SD card. I can insert another card with more files, or chroot to other external storage. The rootfs is in RAM. Been booting RPi with tootfs in RAM since 2013.

SD cards are not reliable for frequent, small writes, IME. Certainly worse than USB sticks. I wish RPi offered the option to boot from USB. Even an option to use a SD card to eMMC adapter and boot from eMMC would be an improvement.

Yah, well, the other points with early Raspberries were underpower/undervoltage due to shitty design and signalling of its own circuitry,

only to be compensated with the one-and-only-official-wall-wart-with-attached-cable,

bad config/buggy design of the upstream-driver itself,

fixes of those only rolled out with much delay into their 'OS', and so forth.

Also https://www.bunniestudios.com/blog/on-microsd-problems/ (2010),

& https://www.bunniestudios.com/blog/2013/on-hacking-microsd-c... (2013)

& https://media.ccc.de/v/30C3_-_5294_-_en_-_saal_1_-_201312291... (2014)

and much many more...

Just log to RAM, or something else, than that tiny tempting toy.

That aside flash-fraud is still rampant, no matter what you think you buy from whomever.

Is SD card "quality" really relevant? I've long wondered why it remains the problem only on Raspberry Pi. One quirk of Pi is it doesn't have proper power circuit, likely for legal reasons. Are such design oddities really not have to do with early SD failures specifically on Pis?

A normal-quality microsd is already the same price per byte as a real SSD, so paying 50% more to get a high endurance card is pretty annoying. Also annoying is that the sandisk high endurance still doesn't have a 1TB model.

> you're going to get exactly what you paid for.

And nearly always the cheap cards seem to fail due to firmware shortcomings rather than hardware faults. Ie. the built in wear levelling and error recovery is bad.

Considering firmware is effectively free once written, the fact the cheap cards still don't have good firmware leads me to believe it might be deliberate market segmentation. Ie. "we need to make the cheap cards glitch and fail often, or nobody would buy our expensive cards".

If so, it really raises moral questions about how many peoples wedding pictures have been gobbled simply so some executive can get his christmas bonus...

What specific brands and products have you been using successfully?

In the same vein as this I've wondered for a couple years now what the impact of flash storage longevity is on mobile phone performance over time. Felt like my Samsung S8 was very snappy when I got it, yet a couple years later things that used to be fast - like finding specific music, scrolling through the photos in my gallery, etc. - had slowed down considerably.

Could also just be software updates or other things causing this but there should be some component of decreasing performance caused by wear on flash storage.

What kind of intense read/write nature you are talking about in a video game console? It just reads the game ROM from storage and executes it, there is nothing to write back, the game is not being modified in any way while playing. All these talks about wearing out sdcards in game consoles or raspberry pi devices in my personal opinion are partially because of people encountering poor quality cards - counterfeits. There is an sdcard in my car camcorder which must have seen thousands of full write cycles and still has no issues functioning despite all the operating temperature differences it endures due to weather seasons.

Safe is a multifaceted term. Essentially these storage media (I'm more experienced with solid state but HDDs may be included) the probability the data you wrote is the data you read is a function of how many program/erase cycles, how long ago that was, and naturally the part's specifics. For example, a lot of NOR flash is rated to 10 years at up to 100k cycles. But devices > 10 years old rarely make the news for their flash being dead. On the other hand, I believe there was a Tesla fiasco where their logs were wearing out the flash prematurely.

There's usually trends to look for in regards to that third factor. The lower the # of bits per cell, the higher probability the voltage level is still working the right range. Which is why so much flash is still SLC or pSLC capable. Usually this is more industrial. Then you have entirely different technologies altogether. NVRAM/FRAM/MRAM are various terms for extremely high (or infinite) read/write technologies while still being non-volatile (keeps its data with power off). I don't know how much of a drop in replacement those are. I think LTT had one of those on a flash drive a while back https://youtu.be/oJ5fFph0AEM, but it's so low capacity it'll probably be useless.

It may be possible to hack something up with a MR5A16A. It's a whole 4 MB but has unlimited endurance and over 20 years of endurance. It looks like it has more of an SRAM interface than NAND, but should be capable of saturating a USB high speed link. The drive would likely cost $75? TBH if there was a market it may be a fun project.

If you sacrifice some endurance you can go up to 1Gb per device which might be interesting. But the cost scales.

I’ve run a modded Wii U for ~5 years (mocha cfw -> cbhc -> tiramisu -> aroma) and have always used a usb flash drive, but I did have one fail and just assumed it was a bad unit — I could well imagine the write patterns being particularly hard on them though.

Probably overkill, but I wonder if anyone has experimented with setting up a raspberry pi or something to pass through access to a network share over USB, that way you could have all the data on a RAID array with a proper automated backup strategy somewhere.

Considering SSD prices have crashed it’s the only way to go IMO, it solves literally all of the problems with other iptions like power draw for hard drives and longevity and speed over flash drives

Why is there that much writing? I would imagine a game system reads billions of times as much data as it write.

Most eMMC chips (basically the chip version of an SD card) can be configured to work in pseudo-SLC (pSLC) mode. This halves the capacity but improves the write endurance by several times.

a very visible increase in price and decrease in capacity

Unfortunately SLC costs disproportionately more compared to MLC, TLC, and now QLC -- the actual die cost is only 3x for SLC compared to TLC of the same capacity, but the prices are closer to 10x or more.

Related: https://news.ycombinator.com/item?id=40405578

I back up important things on SLC USB-A flash drives and write refreshed copies at least annually. The drives are small (<=8GB), expensive, there are only a handful of manufacturers (mine's an ATP), and you're probably ordering it from Digikey or Mouser. SLC will supposedly hold data at rest longer, and USB-A means I can find readers for at least another decade. We'll see if retention at rest is actually good.

These don't use SLC, they use TLC. SLC is hard to find in SD cards and SSDs due to cost.

2010, and 2013.

This is interesting, I got gifted an one of those hydroponic systems. The thing was 2 years old. Runs on a Raspberry Zero. The issue? SD card corrupt. I got an image from someone else and fixed it with that.

What's worse is that these things are connected to the internet (with VNC installed!), and they don't do updates...

The system is awesome, but I VERY quickly moved it to a separate VLAN.

These haven't failed for me:

https://www.digikey.com/en/product-highlight/a/atp/advancedm...

I'm cynically guessing it's down to a relatively simple workaround in the SD card firmware that fixes this very common corruption on power loss while writing. Or maybe that combined with a 0.1 cent capacitor.

Writes aren't the only things that can degrade data stored on NAND flash. Not sure how SD cards are mitigating read disturb errors, for example.

I've seen the same. I don't think it's the reboot. My understanding is that NAND undergoes wear-leveling even when it is read only. The card shuffles data around its storage even when it hasn't been written to. And the firmware is unreliable.

Are there other SBCs / SoMs that are as widely used with SD cards though? That's certainly a source of bias.

From what I understand, Flash manufacturing and management during operation are black arts at this point and nobody wants to give the smallest clue for anything related to Flash management and specifications.

For example, Crucial (Micron) doesn't give any TBW for their external SSDs, giving indications that they're using mixed-binning as long as the speed specs are satisfied. Same for lower level Kingston (NV series) SSDs. At least they openly say that the drives can wildly differ from batch to batch (and oh boy, they do).

As the industry is pinched by customers for more capacity, QLC becomes the norm, TBW numbers are continuously hidden, and you're only left with the internal endurance counters, if you can access them.

Controllers are in the same boat. Wear leveling, write amplification, flash monitoring are all left to whims of the controller designers, resulting in strange situations.

Off-shift/dark production is another problem, but it's not new by any means. BunnyStudios has a great write up which has been linked a couple of times.

ZFS (or btrfs) will do that for you, no hardware RAID required.

Most pro DSLRs have two SD card slots and will also do it (at the firmware level) if you toggle the appropriate option (usually the options are RAID 1 or a unionfs-like "use both SDs" option).

Wouldn't a USB hub and, say, BTRFS do the job?

It's high endurance compared to TLC and QLC, which make up >99.9% of flash sold nowadays. Sure SLC is even better but it's all relative.

>All microSD cards have a high failure rate.

You can buy genuinely reliable microSD cards, if you really need them. Delkin, Innodisk, Swissbit and others make industrial microSD cards with SLC flash, ECC, SMART and power loss protection. Capacities are small and you'll pay a steep premium, but they legitimately have endurance and MTBFs that compete with conventional SSDs.

Ref 2: if you buy from Amazon, you never know if you get a genuine card. Even if you shop from an official seller, as inventory is commingled so you might as well get a fake one from another seller with the same SKU.

Big problem in action cam related circles, where lots of people have broken recordings due to fake cards.

Important thing you should be aware of: not all counterfeit cards fail a format/f3 test.

I recently bought a very expensive Sandisk Extreme UHS-II V90 card from Amazon. It passed without any issue when doing a full capacity check, but was still fake because they were using slower (150mb/s vs 300mb/s) flash.

The average user[0] would never know, because it was definitely “faster” than other cards and maxed out the UHS-I reader in my MacBook Pro. I returned it and bought from my local camera store (Henry’s) and the performance difference was very obvious.

[0]: I guess you could argue that the average user wouldn’t be buying a $200 V90 card, but I still think you could fall victim to this if you didn’t explicitly own a dedicated UHS-II reader.

1) I have ~7 cards (all from China and Sandisk, solely because Sandisk has a website where you can verify the card is genuine) that are in daily 24/7 use for 6-8 years with no issues (mounted in rw mode) 2) ... 4) that's true for any storage media

If you ever tried running uSD card in SDR104 mode, you'd notice that they tend to heat up way more than in lower speed interface modes. So for longetivity, I guess it's better to run them at HS mode (which is just 50MHz), or at least lower the SDR104 bus frequency from 200MHz to something lower.

Ref 2

You mean a simple reformat with fat? Or what’s in your opinion the best test when getting a new SD card?

That can just as well be marketing or a way to pad the price.

64 GiB microSD still costs ~$14 locally, but the same thing can be had for $4 from China without any warranty.

They stick endless limited warranty on it and increase the price so much that it's economical for them to just replace a few cards that people will actually bother to return, and still make profit. And warranty will tell you nothing about quality.

In fact on many products you can explicitly choose to pay more for longer warranty.

For maximum clarity, is there a positive or negative relationship between warranty length and longevity?