Buy a real brand: people have there own opinions on this, but to me this means Sandisk, Samsung or Verbatim. Had a bad experience with Lexar once but as always ymmv.
Buy from a real retailer: this means B&H or Adorama or a not-shady brick and mortar store. Amazon will happily ship you counterfeit cards that will crapp out when you need them most, like ebay will. This is coming from someone that chooses to buy a ton of their electronics from ebay, Aliexpress or street hawkers.
A cursory glance around AliExpress shows SD cards with “decorative” labels - and straight up fakes. The problem you get is that any joe blow can buy from Ali- resell on Amazon or elsewhere - and be truthful in saying that he was trusting his seller.
I tried a couple of FAT32 formatted 16GB SanDisk microSD that have a "Lifetime" warranty in an OpenWRT-based router that has a microSD card slot. I managed put them both into unrecoverable "read-only" mode by letting some daemon write to them unconditionally.
They were purchased from a large electronics retailer not Amazon.
I normally do not use SD cards or USB sticks for non-interactive, frequent writes. I usually write to them manually (i.e., interactively), either storing files or dd'ing bootable images. For example, I am not one of those people who tries to use an SD card as a substitute for a HDD in an RPi. I only use tmpfs for non-interactive writes.
Is there any reason I should not conclude that these cards are not suitable for high frequency and high volume of writes.
I've had always bad luck with Sandisk, both CF and SD/microSD cards.
Sure every brand will have lemons, but if you’re seeing consistently bad “SanDisk” cards.. you are pretty certainly not getting genuine product. Find a reputable supplier (which is absolutely not Amazon)
Both Adorama and B&H sell on Amazon too, but for photo/video gear I would go to B&H direct.
If anyone chooses to order memory cards or the like from Amazon US specifically for whatever reason, I find that at least an hour reading reviews and surveying listings is required for me personally to be reasonably hopeful I will get what I want. Trying to spot dishonest reviews or signs that older reviews are for a different product (swapped listing). I imagine if I were in the US I could simply order multiple product variations from different listings & sellers and then pick the most genuine-looking one, returning the rest, but that would be a major hassle when ordering overseas.
There are higher speed classes past class 10.
Give me 4 numbers: Read and write speeds, each in terms of minimum sustained transfer rate and minimum random IOPS.
Also worth noting that these cards (with the exception of xD, which is just a packaged raw NAND flash) have a complete embedded system in them too: https://www.bunniestudios.com/blog/?p=3554
: It also opens the door for accidental formats.
With modern TLC flash any card without wear leveling would fail pretty quickly.
Wear leveling is actually a major problem for applications where power might be suddenly cut, because if it happens while the wear leveling is running then the block allocation table can be corrupted which leaves the whole card unreadable. It's a pretty common complaint among i.e. raspberry pi users who tend to unplug them without shutting down.
From Wikipedia (marked with "Citation needed"):
> The SDHC format, announced in January 2006, brought improvements such as 32 GB storage capacity and mandatory support for FAT32 filesystems.
How dumb storage device can refuse to support FAT32?
Fun fact: SD cards support SPI interface and can be easily connected to cheap microcontrollers.
SDHC and SDXC are identical at a protocol level.
I would not recommend using SPI mode.