SDcard wear leveling and translation layers (2014)

Post by Scoutmaster » Thu, Aug 01, 2024, 9:18 PM UTC

weweweoo wrote: post #33

goodburb wrote: post #28

Earlier quoted context omitted.

Maybe there are more lemons with SD cards. The fact that they're used in dash cams, exposed to high temperature thermal cycles, and recording tens of terabytes of data which can be more than the typical consumer HDD/SSD in it's lifetime is quite impressive.

Recently I found a long lost go-pro style camera using metal detector, after it had fallen off an RC plane, which crashed into a tree in dense forest. Over nearly a decade the camera had been buried several centimeters into the ground, and the card inside the camera wasn't particularly well protected (just an open slot, not waterproof or anything), which made it exposed to lots of water and freezing winters for nearl…

I recommend everyone take a picture of their contact information with their digital cameras, that way if it gets lost and found, people know who to at least send the pictures to if the camera is destroyed.

I imagine the RC plane's owner would get a real kick if years later the camera was found and they got the footage back.

(I used to work at Philmont Scout Ranch and would do a lot of detective work to get people their cameras back.)

Post by SideQuark » Fri, Aug 09, 2024, 4:45 PM UTC

st_goliath wrote: post #62

SideQuark wrote: post #55

Earlier quoted context omitted.

> I was talking about bare NAND flash Same here. > None of the projects you describe sound "cheap" or like they involve devices first-and-foremost optimized for cost A lot of them are low cost PIC microcontrollers, which are super cheap, and the lowest cost MCUs were chosen precisely because at large commercial sale scale saving pennies on HW is very important. The reason we went to such lengths to reuse bits at the…

> low cost PIC microcontrollers ahhh, I think there's the source of our confusion: I suspect you are actually talking about NOR flash? NOR flash is physically organized different from NAND. It typically does allow single word/byte or sometimes even bit level accesses, like you described. NOR flash is also much more reliable, often not needing any wear leveling at all. The downside is that NOR flash has orders of magn…

> ahhh, I think there's the source of our confusion: I suspect you are actually talking about NOR flash?

Nope. PIC has on device NOR (which I've tested), and often has external NAND flash (depending on design choices), such as using SDCard interfaces.

Here's [1] a Micron tech doc on their NAND chips stating quite clearly they allow exactly what I described doing above: "A NAND Flash block is 128KB. Erasing a block sets all bits to 1 (and all bytes to FFh). Programming is necessary to change erased bits from 1 to 0. The smallest entity that can be programmed is a byte."

There's plenty of manufacturers and chip types that guarantee one can do this. It is tech notes like that led me to do some testing to see if devices fall into spec on R/W cycles before death when evaluating which chips to ship in consumer products that need this.

[1] https://user.eng.umd.edu/~blj/CS-590.26/micron-tn2919.pdf

Re: SDcard wear leveling and translation layers (2014)

Re: SDcard wear leveling and translation layers (2014)