Sandisk (and others) market their high endurance memory cards as being temperature-proof, waterproof, shockproof and x-ray-proof (which I believe they all are anyway) and guarantee write enduring in hours of recording time (which is a little meaningless in terms of digital video).
There doesn't seem to be any technical details with respect to these cards. Would they just include more memory for wear-leveling, use a different type of NAND or is it just marketing BS for plain old SD cards?
Yep bitrot is more of a problem since the write endurance tends to be handled by the controller chip remapping pages as they get written too much (unless you really write all the time).
What you probably get in the better cards is the more reliable less crowded flash technology.
They put varying amount of data in flash cells:
1 level: SLC flash
2 level: MLC flash
3 level: TLC flash
4 level: QLC flash
More analog levels you use inside a cell the sooner the cell might leak some charge and change state. So SLC is most reliable where the cell is just a binary 1 or 0. Most flash storage right now uses TLC, but most of the new high capacity flash is QLC. If you buy a fancier more expensive SSD (Such as the Samsung 8xx 9xx PRO) then you get MLC flash in it. Getting SLC flash in a SSD is pretty hard unless you buy some specialized enterprise SSDs that cost an arm and a leg.
So if you can get a memory card with MLC flash in it that will help reliability as opposed to the QLC garbage they are now rolling out everywhere for consumer stuff.
I can understand that multi-levelling (more bits per cell) reduces your "noise" (bitrot) tolerance, but what about other factors?
Surely all of the other fab parameters (cell size, material, quality) would have just as much (or even more) impact on things like cell charge leakage rate? From what I've read there is also ECC going on to try and correct these problems, something that I suspect everyone will implement to different degrees.
ie is there any data to suggest that SLC/MLC/*LC is the most important thing affecting shelf life for flash?
I probably should elaborate, I intend on using these cards in my car's "dashcam". It won't be recording all the time, only when driven. Some 2-3 hours per day.
I don't know how the finer manufacturing process affects it, but the manufacturer does have motivation to go for reliability in MLC and SLC flash.
As they go to MLC or SLC they get less bits per cell so this flash becomes significantly less cost effective already. So the only reason you would manufacture MLC flash array today is because of reliability, if its not reliable then you might as well use QLC and get the most storage for the silicon area.
But ECC has been present in flash all the way from back when flash chips only held a few MB of data. They knew its not as reliable as other memory types. What made it even worse is that typically NAND flash did not have a controller built in. So the "ECC" feature was simply a few extra bytes on the end of each page, you had to implement your own ECC to make use of the extra storage area. Same with bad page remapping. This is why everyone now uses eMMC memory as that's basically a SD card on a chip where its built in memory controller takes care of all this crap.
For example bitrot killed Keysight MSOX2000 and MSOX3000 because they didn't use ECC for the initial bootloader and eventually bitrot would flip a bit in the bootloader and the scope would become bricked. They would repair your scope for free if you had this fault (Likely involved flashing it via JTAG and then loading the new firmware on)
I probably should elaborate, I intend on using these cards in my car's "dashcam". It won't be recording all the time, only when driven. Some 2-3 hours per day.
Ah, ignore my ramblings about shelf life then.
I'm having troubles finding benchmarks of people testing microSD card endurance. This makes me uneasy.
Caution: many vendors are describing their high-endurance card lifetimes in terms of "hours of dashcam footage". It's worth digging further to find what mbps they are referring to & multiply it out.
Something important in this discussion: larger cards tend to have higher endurances. Eg
https://transcend-info.com/Products/No-727 :
16 GB: 3,000 hours
32 GB: 6,000 hours
64 GB: 12,000 hours
This brings up the question of "should I spend X dollars on a smaller 'high endurance' card or the same X dollars on a bigger 'normal' card?"
Caution: many vendors are describing their high-endurance card lifetimes in terms of "hours of dashcam footage". It's worth digging further to find what mbps they are referring to & multiply it out.
This is the issue I'm having, most vendors don't specify it (probably because 99% of consumers don't care). The camera I've ordered only specifies the codec (MPEG4), not the bitrate. I'm assuming it's a few Mbps for full 1080P video.
Even still, I'm not enjoying the fact that memory card manufacturers choose to market these cards in terms of "hours of video recorded". That figure is arbitrary and really doesn't mean anything. How would they even measure that in case of failure?
My assumption is that it's all marketing bullshit, the same cards packaged differently but at a higher price. There is probably enough profit margin built-in to provide a replacement or two to end-users without asking any questions. Really, if someone buys a 64GB card today, will they really be using it in 10 years time? Probably not. 64GB will seem small and insignificant by then.
In terms of pricing, I can buy a Lexar 64GB Class 10 card through my suppliers for $19.80 vs $54.87 (retail) for a Samsung 64GB "High Endurance" card of similar speed.
Wait for a sale and you can get SD cards for way cheaper.
Sandisk probably not, Panasonic industrial or Swissbit is probably yes.
The SLC flash is not the only difference for these cards, they have different write algorithm and garbage collector in their firmware.
And properly written datasheet, tested to IEC 61000, and so on. Reliability is night and day.
I picked up a cheap 128GB microSD card for about 14 bucks on Amazon and the prices keep plummeting every day. If this is for your dashcam, then I suggest going for whatever is cheap, and just replacing it if you manage to use it long enough to kill the thing. Flash isn't good for archival storage, and while magnetic storage is often better, if you care about your data, it should never stay on one device for a long period of time.
Yeah for only being used in a dash cam i wouldn't be so concerned with cheap cards.
Dash cams tend to just write linearly over the card and then loop around when it comes to the end. This is as gentle as possible on flash because all the write activity is nicely spread out. Also for video if you loose a few kilobytes in the middle of a video file the file still plays fine. You do tend to get some visual garbage where the missing data is but it typically won't result in completely blank frames and will recover completely when the next keyframe comes around.
Tho if you get corruption in the video file header then you can end up with an unplayable video file but a bit of hex editor work can likely just copy the header from another working file and get it to play again. Its the corruption in the filesystem tybles that is the most problematic since it can destroy the entire partition, but FAT32 does keep a duplicate so it can recover from some corruption.
And if the card dies completely the dashcam will likely start throwing error messages the next time it tries to record. Tho i have seen cases where old near dead SD cards would lock up and stop responding to the host. In a android phone this can cause the whole phone to lock up because it responds enough for it to think the card is still there, but takes literally forever when asked for data.
I probably should elaborate, I intend on using these cards in my car's "dashcam". It won't be recording all the time, only when driven. Some 2-3 hours per day.
Ah, then forget everything I wrote...
I thought it was one of those cases, when some clueless schmuck designed an SD card into a high reliability embedded system, and you need to clean up, and improve the 1000 hrs MTBF.
The L in xLC is actually deceptive. MLC is not two level cell, it's actually two bit cell, or 4 level cell. Similarly, TLC is 3 bit cell, or 8 level cell. QLC is, well, 4 bits, or 16 levels.
It's pure marketing deception. Apparently "5 level" flash is coming, which actually stores
32 voltage levels per cell:
https://blocksandfiles.com/2019/08/07/penta-level-cell-flash/I'm still not at all convinced that this is a good idea, and it's almost certainly planned obolescence --- with "QLC" you get a 4x increase in capacity for 1/16th the endurance, and 5bpc will be 5x the capacity but have 1/32nd the endurance of SLC. Put another way: would you rather have a 1TB SSD that lasts 32 years, or a 5TB SSD that costs 1/5th as much, but lasts only 1 year?
I ended up going middle of the line. I bought some 32GB Transcend cards. They were cheap and I've used them before for long periods in a hot car with them surviving just fine. During summer in Australia, the interior of a car can reach above 80 degrees Celsius in some cases.