51–60 of 72 posts
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It isn't. Before a chip has firmware loaded, it can't decode filesystems.
Even after a chip has firmware loaded, which controller can make logical sense of a filesystem?
exfatprogs can pack bitmap with table for SDHC and lower: https://manpages.debian.org/experimental/exfatprogs/mkfs.exf...
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Pages that are already written cannot be overwritten, at least not without a full block erase, so it has to do a remap to append data. Directly logging to an SD card (i.e. lots of small writes) is the fastest way to destroy it.
As I understand it, you need a block erase to change bits from 0 to 1 then you can selectively set bits back from 1 to 0. Couldn't you perform a file append without the need for a block erase? By keeping the unwritten area as all ones until written?
At a conference, I once met somebody who said his team had the joy of dismantling broken SD cards and figuring out why they broke. One of the anecdotes I distinctly recall was about a batch of cards that (for obvious cost saving reasons) used the actual data flash to store its own firmware as well. IIRC due to a bug in the wear leveling accounting, once the card got sufficiently full, the wear leveling code ended up…
Have an SD card that was copying file on to and in the middle of transfer the card went kaput and hasnt seen since. No machine I try it on even acknowledges it existence. The card is almost a decade old at this point but is there a way to recover data ?
10 years without power makes me think most of it wont be recoverable even if they can get to the data on it, but then again it depends on a lot of factors when it comes to flash memory.
At a conference, I once met somebody who said his team had the joy of dismantling broken SD cards and figuring out why they broke. One of the anecdotes I distinctly recall was about a batch of cards that (for obvious cost saving reasons) used the actual data flash to store its own firmware as well. IIRC due to a bug in the wear leveling accounting, once the card got sufficiently full, the wear leveling code ended up…
Man, I'd love to work in that team for a year. I've had so many SD cards fail on me (most recently a 1TB SanDisk Extreme which was used in my Steam Deck) and it feels like most of them are junk.
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>> Couldn't you perform a file append without the need for a block erase? > You cannot do single byte writes on NAND. This isn't true - that the OP wrote here certainly does work (at least for many places I've tested and used it). I've used it to do all sorts of low level logging in small devices (and I've thoroughly tested many, many chips to complete destruction to see how things degrade). I have not yet seen a pla…
I was talking about bare NAND flash, not eMMC or anything otherwise "fancy" with builtin FTL. What you say is certainly true for those. None of the projects you describe sound "cheap" or like they involve devices first-and-foremost optimized for cost, and are unlikely to involve such dirt-cheap, raw NAND devices that are becoming increasingly rare even in the super-cheap embedded space. The original context of the di…
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 lowest level is because of needing the lowest cost devices on those projects.
Some were higher end, but I think it's more useful on low end chips.
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ZFS can do this. Just set copies=2 on a dataset, and it'll always keep 2 copies of everything written thenceforth (with ~twice the storage usage). And since it's a dataset setting instead of a pool setting, it can be applied selectively on a storage device. "Oh, those photos are also backed up to Google Photos. It's maybe not ideal, but it's a lot of data and not worth keeping 2 copies those locally, so I'll leave th…
Is there even that much value to keeping multiple copies on the same device ? I fail to see what this adds over backups which can be done with any filesystem.
Backups are better (if they actually get done, and if they are actually usable for recovery).
Backups + RAID is better yet.
But OP asked for a particular set of things that do not have any direct relationship to the traditional concepts of either backups or RAID, and ZFS can provide that set of things using copies=2.
It isn't for us to decide the value of this for them.
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Have an SD card that was copying file on to and in the middle of transfer the card went kaput and hasnt seen since. No machine I try it on even acknowledges it existence. The card is almost a decade old at this point but is there a way to recover data ?
Best to consult a data recovery specialist, will cost you an arm and a leg though. 10 years without power makes me think most of it wont be recoverable even if they can get to the data on it, but then again it depends on a lot of factors when it comes to flash memory.
Earlier quoted context omitted.
Pages that are already written cannot be overwritten, at least not without a full block erase, so it has to do a remap to append data. Directly logging to an SD card (i.e. lots of small writes) is the fastest way to destroy it.
That could explain why my dashcam is working fine after ten years whereas my previous job's IoT devices regularly ate SD cards. (Then again, the IoT devices were also overheating badly whereas the dashcam was designed for its purpose, kept cool while running, and runs on a low duty cycle) What are you supposed to do, then? Buffer up writes and accept that you'll lose logs a minute or so before a power outage? As much…
Does anyone have access to the full specs of some SD cards? To get access to the full specifications it seems like you're forced to join the SD Association: 2500$ p/year
What is the point of charging for it, especially such an outrageous amount?
It's $6.84 per day for a membership.
If that's an outrageous amount to you, then: Please remember that you are absolutely free to direct your rage into creating your own competing portable flash storage systems, and to license them in any way that you wish.
You may even include a free pony, if you choose. It's your world.
At a conference, I once met somebody who said his team had the joy of dismantling broken SD cards and figuring out why they broke. One of the anecdotes I distinctly recall was about a batch of cards that (for obvious cost saving reasons) used the actual data flash to store its own firmware as well. IIRC due to a bug in the wear leveling accounting, once the card got sufficiently full, the wear leveling code ended up…
Man, I'd love to work in that team for a year. I've had so many SD cards fail on me (most recently a 1TB SanDisk Extreme which was used in my Steam Deck) and it feels like most of them are junk.