> SD cards are divided into sections, called Application Units (or AUs). The Video Speed Classes in particular require certain commands to be issued to it to put the card into Video Speed Class mode and to specify which AU the host will be writing to. The host is then supposed to write only to that AU, in a sequential fashion (skipping over any blocks that are already in use). Once the host has reached the AU, it must issue another command to specify which AU it will be writing to next
This is something I didn't know about SD cards. Does SD card firmware mark blocks as belonging to a specific "Application Unit"? Seems to be some sort of "preallocation" scheme.
It does -- but the problem is that there are very few readers out there that are supported by the Linux mmcblk driver. Most of them just present themselves to the system as generic USB block devices.
> Does SD card firmware mark blocks as belonging to a specific "Application Unit"?
Yup. Basically cards are divided up into application units, and application units are divided up into recording units. Where they're physically located on the card is opaque to the host -- so yeah, it can rearrange them as needed.
Seems possible that by charting it, you could find a "bathtub curve" (early failures/steady state/failures due to use) of failures, probably more than one curve breaking up by category--tiny "industrial" cards made for endurance are unsurprisingly surviving the longest, and counterfeits and (some but not all!) unknown brands are at the bottom. It would be interesting to also see the data on cards that haven't failed yet, i.e. how many write cycles they've survived so far.
(You can sort the table at https://www.bahjeez.com/the-great-microsd-card-survey/all-mi... by cycles until first error to see what I mean. Love the Bart Simpson card coming in at #8.)
One thing the reported averages already show, which is more about reliability stats in general than about Flash, is that the average write cycles survived is way higher than, say, the cycle count after which you'd see 5% of devices fail. The lower "n% will fail" number might be what informs the TBW spec on the box. So if you're able to handle failures gracefully and run drives 'til they drop, that probably adds substantially to how long you can run each device.
These endurance tests aren't testing retention much at all; they answer the question "how many cycles can the flash go through before it can't hold data for the very short amount of time it takes to read it back again on the next pass", which is not surprisingly much higher than e.g. the number of cycles before which the data will disappear after 3 months. The cells can be so worn and leaky they erase themselves within a few hours, but as long as that's more time than it takes until the data is read back, this test will still consider that successful.
- A powerful blender. Will it blend?
- Two sets of pliers.
- A taser. That's how I upgraded many Radio Shack radio scanners.
- A well ventilated fireplace, fire-pit, oxyacetylene welding torch using rosebud tip.
- Train tracks.
- Create a Youtube Channel, take sdcard to a shooting range that lets people borrow their Abrams tank or Howitzer cannon. Blast the SD card. Monetize your channel to make up for the cost of renting the tank and buying many new sd-cards.
If you meant it had to be a piece of software, even if you can manage to make it read-write there may be data left behind.
My Tikka T1x can do it. At 50 yards.
It's more useful for me to know that if I see brand X saying I'm buying a class 2 32Gb card, I'm getting a card that reads at 2GB/s and has 32GiB of storage, but if I buy a brand Y class 10, I'm going to be able to read at 5MB/s and only 16GiB is usable.
userbinator•7mo ago
brudgers•7mo ago
according to the SD Physical Layer Specification, “Card Capacity means the sum of User Area Capacity and Protected Area Capacity”
Which makes sense from a manufacturing perspective...what hardware is required to make the thing?
Also makes sense from a marketing perspective...bigger is better right?
And legally, it's right there in the fine print...that's what "SD" means your honor.
bell-cot•7mo ago