I think the most surprising thing from this article is that microSD cards may not even have a decimal amount of space; while all the hard drives I've encountered have at least that much if not somewhat more, apparently the expectation that a 32GB microSD card be able to store 32,000,000,000 bytes isn't the norm. How do the manufacturers find a way to explain that? It's definitely bordering on fraud at that point.
If you're surprised by that...stay away from magnetic tape storage. The headline "capacities" of those are usually based on optimistic data compression ratios.
I am really surprised there isn't a linux command out there that allows you to send low-level CMD's to an MMC controller. I thought mmc-utils did.
> 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.
Flash endurance gets a sort of odd amount of discussion on the Internet, and this adds to the small amount of public data from running lots of Flash devices to exhaustion. (MicroSD != SSD, of course, but it's something.)
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.
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.
I have a genuine Samsung SDXC card that has gone into read-only mode. Even a low-level format does nothing to the data and fails out around 90%. Other than the obvious hammer, are there any tools capable of destroying the data?
are there any tools capable of destroying the data
- 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.
I think the most surprising thing from this article is that microSD cards may not even have a decimal amount of space; while all the hard drives I've encountered have at least that much if not somewhat more, apparently the expectation that a 32GB microSD card be able to store 32,000,000,000 bytes isn't the norm. How do the manufacturers find a way to explain that? It's definitely bordering on fraud at that point.
from the fine article:
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.
If you're surprised by that...stay away from magnetic tape storage. The headline "capacities" of those are usually based on optimistic data compression ratios.
I am really surprised there isn't a linux command out there that allows you to send low-level CMD's to an MMC controller. I thought mmc-utils did.
> 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.
Flash endurance gets a sort of odd amount of discussion on the Internet, and this adds to the small amount of public data from running lots of Flash devices to exhaustion. (MicroSD != SSD, of course, but it's something.)
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.
I have a genuine Samsung SDXC card that has gone into read-only mode. Even a low-level format does nothing to the data and fails out around 90%. Other than the obvious hammer, are there any tools capable of destroying the data?
> are there any tools capable of destroying the data?
My Tikka T1x can do it. At 50 yards.
are there any tools capable of destroying the data
- 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.