
Mistakes to Avoid When Buying a MicroSD Card (2018) - peter_d_sherman
https://www.makeuseof.com/tag/5-mistakes-avoid-buying-next-microsd-card/
======
brazzy
> Counterfeit cards correctly report the capacity shown on the packaging, but
> actually contain far less. You won’t notice this until the card fills up
> unexpectedly quickly.

Oh, it's much worse than that. Counterfeit cards are often manipulated to lie
to the OS about their capacity as well. They don't "fill up" at all, they just
throw away your data, or overwrite it silently.

~~~
MisterTea
That is downright evil. I suppose in order to find an evil card one would have
to fill it with a file and then verify that files integrity, a very time
consuming process form larger cards.

~~~
fheld
the German Computer magazine heise made a tool[0] to verify the capacity by
filling it up with random files:

[0]
[https://www.heise.de/download/product/h2testw-50539](https://www.heise.de/download/product/h2testw-50539)

~~~
gruez
You don't even need such a tool if you're on mac/linux or have msys/cygwin/WSL
installed on windows. just do

    
    
        dd if=/dev/urandom bs=1048576 count=5000 | tee test.bin | md5sum
    

(substitute bs=1048576 count=5000 with the actual size of the sd card) then do

    
    
        md5sum test.bin 
    

and check whether the two hashes match.

~~~
rlpb
Watch out there: the kernel will cache what it wrote out, and all you'll end
up checking is the cache and not the card. dd has a "nocache" option but it's
only a request. "direct" might work; I don't know.

Maybe someone will come along and provide references to a a definitive answer
on what the behaviour will be.

My point is: it's not trivial to ensure that you're actually testing the right
thing.

~~~
bryanlarsen
The trivial solution is to to do the two MD5 sums on two different machines.

~~~
pmoriarty
Wouldn't removing the card, putting it back in on the same machine and then
doing your second hash be sufficient?

------
cbanek
> hardware that supports microSDXC slots won’t automatically support every
> size of card in this format. The Samsung Galaxy S9, for example, officially
> supports cards up to 400GB. There’s no guarantee that your 512GB card will
> work.

This part drives me nuts. I wish devices would just follow the spec, and
accept up to the maximum capacity. But it seems like device manufacturers end
up testing the biggest card when they make the device, and as time marches on,
you have to search Amazon reviews to see which cards work and which devices
have hardcoded smaller limits on capacity.

~~~
Wowfunhappy
> But it seems like device manufacturers end up testing the biggest card when
> they make the device

I mean, they can't test hardware that doesn't exist yet, so what is the
alternative?

If there's a hardcoded maximum, that's one thing, but we don't know that's
what is going on, do we?

~~~
osamagirl69
The lack of available hardware to test hasn't stopped PC manufactures from
supporting media larger than available for a given interface.

There are occasionally hiccups, like the whole debacle where the MBR partition
table (from 1893) was limited to a few terabytes and the industry switched
over to GPT, but even today if you put in a >2TB disk into an ancient machine
that does not support GPT it can usually at least use the portion of the disk
that it can address.

Just read the spec and write your software to support it. It is not like we
are asking for support of terabyte SD cards on machines released with the
maximum SD card size was 128MB.

~~~
Digit-Al
> MBR partition table (from 1893)

I still think it's quite an impressive feat to support that much data before
computers even existed though lol

~~~
mixmastamyk
Maybe not, Babbage might disagree:
[https://en.wikipedia.org/wiki/Analytical_Engine](https://en.wikipedia.org/wiki/Analytical_Engine)

------
ohazi
Also A2 performance requires operating system level support, and all of these
tips go out the window if you're using the card for a Raspberry Pi.

[https://www.jeffgeerling.com/blog/2019/a2-class-microsd-
card...](https://www.jeffgeerling.com/blog/2019/a2-class-microsd-cards-offer-
no-better-performance-raspberry-pi)

[https://www.jeffgeerling.com/blog/2019/raspberry-pi-
microsd-...](https://www.jeffgeerling.com/blog/2019/raspberry-pi-microsd-card-
performance-comparison-2019)

------
jsjohnst
> MicroSDXC cards use the exFAT system by default. Windows has supported it
> for over a decade, but macOS only since version 10.6.5 (Snow Leopard).

Snow Leopard was released a decade ago[0], so seems like their choice of
wording is indicating a bias there.

[0] 10.6.5 was released in Nov 2010 however per Wikipedia, so almost 9 years.
Still feel my point remains.

~~~
Zenst
Worth adding that exFAT has aspects that Microsoft hold patents for. Yes they
do license for a flat fee, though not aware Apple holds such a license. Also
it wasn't until circa 2009 that the SDCARD collective adopted it as a
standard. That and wasn't until 2013 that a GPL Linux driver was available.

So yes, very unfair to bash Apple about over this, you raise valid concerns.

[https://en.wikipedia.org/wiki/ExFAT](https://en.wikipedia.org/wiki/ExFAT)

~~~
gumby
> Worth adding that exFAT has aspects that Microsoft hold patents for. Yes
> they do license for a flat fee...

When exFAT was released I added this to the Wikipedia entry only to have it
reverted within hours. Hmm.

------
zamadatix
> First, hardware that supports microSDXC slots won’t automatically support
> every size of card in this format. The Samsung Galaxy S9, for example,
> officially supports cards up to 400GB. There’s no guarantee that your 512GB
> card will work.

Does anyone have a real life anecdote of a device which supports a given
version of the standard not be able to use a card of the same version larger
than the device supports? I've yet to run into it and always considered it a
misunderstanding from issues when newer versions of the standard came out with
higher capacity being conflated with what the manufacturer was able to
validate on release date but maybe I've just been lucky.

~~~
jbob2000
Sure. The ecoboost Ford mustang. If you put the engine from a Mustang GT in
the Ecoboost mustang, the crankshaft will explode. You can totally mount the
engine from the GT in the ecoboost, it's the same frame, but the rest of the
car is not engineered to support that much horsepower.

~~~
nicoburns
I think the parent meant specifically with SD cards. I've personally never had
issues using higher capacity cards in devices that didn't officially support
them...

~~~
stevekemp2
Back a few years I bought a large CF-card for a Canon 5D camera, which was
just not recognized.

------
alister
> _We’ve all owned flash memory cards that have stopped working for no
> apparent reason._

MicroSD cards and SSD drives use _exactly the same technology_ (NAND flash
memory), so it’s a mystery to me that microSD cards are unreliable, but SSD
drives are extremely reliable. Genuine SanDisk cards have failed on me for no
apparent reason, but I’ve never had a problem with SSD drives with much
greater usage.

~~~
alibert
It's the controller and the reserved/backup flash. SSD have a powerful ARM CPU
running and optimizing memory cell wear and replacing these on the fly with
the reserve.

SD cards doesn't have that mostly for cost and size constraint.

~~~
rasz
oh but they do
[https://www.bunniestudios.com/blog/?p=3554](https://www.bunniestudios.com/blog/?p=3554)

The difference is in using lowest quality leftover Flash memory.

------
poizan42
The SD Card Association seems really short-sighted when it comes to capacity.
Compare to the world of harddrive where ATA-6 introduced LBA48 which allows
for capacities up to 128PiB all the way back in 2003, while SDUC introduced in
2018 is still limited to 128TiB.

------
egdod
What an absolute mess. I’m a technical nerd, and I can _probably_ do the
research necessary when I need a new card... but we expect ordinary people to
figure it out? Not likely.

~~~
la_barba
Which part are you having trouble with? Seems very simple and straight forward
to me. Your "ordinary people" comment doesn't mean much TBH. It is no
different than buying a tire, you have your speed rating, section width, load
index, maximum inflation pressure, wheel diameter, etc, etc. Wow.. so many
crazy numbers !! How do "ordinary people" ever buy a tire.. :)

~~~
egdod
They don’t buy tires on Amazon. They buy them from someone who’s going to
install them and make sure they fit.

~~~
jolmg
Personally, I always thought knowing how to buy a tire is common knowledge.
They even sell tires at Walmart, and it's not hard to figure out, you just
match the numbers. You've made me curious, though.

~~~
egdod
I’m fairly certain my mom would have no idea how to pick out her own tires.

------
Razengan
Reading about all this kind of shows why Apple must have decided not to
include SD slots in their iDevices.

~~~
tacotime
I think a more likely reason is so that they can charge $150-200 for an
internal storage upgrade of 200-250GB and push their iCloud service. This
wouldn’t work so well for a manufacturer like Samsung who is not as
differentiated from it’s competitors.

------
neves
I've had cards that I could fill with the designated size, but in speed tests
would be slower than the manufacturer specification. Does anyone here also
have these kind of problems?

------
AnthonBerg
My takeaway from the article is that SD cards are a mess information-wise and
that I will continue to not buy or use them.

------
Causality1
Something the article doesn't mention is that there are older SD readers with
firmware limitations that drop their size limit even below the 2GB SD
standard. An example of this is the reader built into the TC1100 tablet pc,
which is limited to cards 1GB in size or less.

------
eitland
Any advice on where to get good cards for Raspberry Pi usage?

I mean it seems like most I have had wear out way in a few months even with
next to no use.

~~~
finchisko
Also make root fs readonly. DietPi distro claims they do it out of box. Same
for openwrt, they mount /var dir as tmps and do writes only there. For
raspbian [http://blog.pi3g.com/2014/04/make-raspbian-system-read-
only/](http://blog.pi3g.com/2014/04/make-raspbian-system-read-only/).

