regarding microSD cards (and flash memory in general)

[Turbonium]

Is flash memory inherently more reliable at lower densities? I am only concerned about reliability here (defined as no data corruption within normal operating conditions and within expected lifespan/cycles), not speed.

Say when comparing a 32GB versus a 64GB microSD card of the same make and model.

I realize this is a very general question, and that the answer could vary depending on the type of flash memory in question, as well as other factors. If it helps, assume TLC NAND, and perhaps MLC NAND (given most consumer-level microSD cards use these types of flash memory, as far as I know).

Note: I'm assuming that the capacity of a given card is a function of density, not the physical size of the memory inside the card. If this is incorrect, feel free to clarify.

 

[paperwastage]

some interesting reading: http://www.bunniestudios.com/blog/?page_id=1022

I’d like to point out to casual readers that the spot price of MicroSD cards is nearly identical to the spot price of the very same NAND FLASH chips used on the inside. In other words, the extra controller IC inside the microSD card is sold to you “for free”. The economics that drive this are fascinating, but in a nutshell, my suspicion is that incorporating the controller into the package and having it test, manage and mark bad blocks more than offsets the cost of testing each memory chip individually. A full bad block scan can take a long time on a large FLASH IC, and chip testers cost millions of dollars. Therefore, the amortized cost per chip for test alone can be comparable to the cost of silicon itself

of course, it might not be true now, but I can definitely see how two chips from the same brand may be made by different manufacturers and behave differently

 

[Turbonium]

some interesting reading: http://www.bunniestudios.com/blog/?page_id=1022

Funny that SanDisk is supposed to be among the best. I expected the same, yet got two defective SanDisk microSD cards, back-to-back, and from different batches.

They seemed to be fine at first, but had issues very quickly after I started using them. I've been wary of getting another microSD card since, regardless of the manufacturer.

 

[Cerb]

Is flash memory inherently more reliable at lower densities? I am only concerned about reliability here (defined as no data corruption within normal operating conditions and within expected lifespan/cycles), not speed.

Long-term, yes. Bigger cells need less ECC, and degrade less from each write.

Say when comparing a 32GB versus a 64GB microSD card of the same make and model.

No. An older generation 32GB SDHC may outlast a current generation SDXC. But, of the same make and model, you're either getting something random (like with Kingston, PNY, HP, Transcend, etc.), or something of the same density, from the same maker.

In general, all SD cards are crap, if you don't get the biggest baddest fastest card out there, compared to other storage. The margins are super thin, and there is every reason to cut corners. I would not trust any SD for backup purposes, even compared to USB sticks, given random corruption I've experienced, that seems to happen primarily to SD. Big names are better than little names, but we got saddled with SD because it was small and cheap, not because it was good, IMO.

 

[VirtualLarry]

In general, all SD cards are crap, if you don't get the biggest baddest fastest card out there, compared to other storage. The margins are super thin, and there is every reason to cut corners. I would not trust any SD for backup purposes, even compared to USB sticks, given random corruption I've experienced, that seems to happen primarily to SD. Big names are better than little names, but we got saddled with SD because it was small and cheap, not because it was good, IMO.

This is very true. I picked up an 8GB SD card for my digicam, and I ended up having corruption on one of the files. Thankfully, it was unimportant, but still... it was worrying.

I absolutely wouldn't run an OS off of an SD card, with the exception of booting a firmware update image for a device. Thankfully, those images are mostly read-only when they boot.

I even have reservations booting an OS off of a USB stick, at least with any stick using TLC memory. (I'm talking about an actual OS install on the USB stick, not a LiveCD ISO imaged to the stick, which again, is mostly read-only.)

 

[Turbonium]

Long-term, yes. Bigger cells need less ECC, and degrade less from each write.

No. An older generation 32GB SDHC may outlast a current generation SDXC. But, of the same make and model, you're either getting something random (like with Kingston, PNY, HP, Transcend, etc.), or something of the same density, from the same maker.

In general, all SD cards are crap, if you don't get the biggest baddest fastest card out there, compared to other storage. The margins are super thin, and there is every reason to cut corners. I would not trust any SD for backup purposes, even compared to USB sticks, given random corruption I've experienced, that seems to happen primarily to SD. Big names are better than little names, but we got saddled with SD because it was small and cheap, not because it was good, IMO.

There's no way I'd ever consider using SD cards for backup purposes. I'm more concerned about my phone freezing, locking-up, and having other issues again when accessing files on a card.

As for the "best" offerings you mentioned being a possible exception, would you say there is an appreciable difference in reliability between the Samsung PRO and the lesser Samsung EVO cards (same generation)?

Link: http://www.anandtech.com/show/7928/samsung-releases-standard-evo-and-pro-sd-cards

Aside from the faster speeds, the PRO uses MLC NAND, while the EVO uses TLC NAND.

 

[Cerb]

The Pro will be faster. Aside form that, I can't say I have any clue, since the main differences, aside from that, are long-term retention, that shouldn't matter.

 

[Remobz]

There's no way I'd ever consider using SD cards for backup purposes. I'm more concerned about my phone freezing, locking-up, and having other issues again when accessing files on a card.

As for the "best" offerings you mentioned being a possible exception, would you say there is an appreciable difference in reliability between the Samsung PRO and the lesser Samsung EVO cards (same generation)?

Link: http://www.anandtech.com/show/7928/samsung-releases-standard-evo-and-pro-sd-cards

Aside from the faster speeds, the PRO uses MLC NAND, while the EVO uses TLC NAND.

I just installed an SD card in my phone and I am getting lock ups and other issues. Looks like the SD card might be the culprit?

 

[Cerb]

I just installed an SD card in my phone and I am getting lock ups and other issues. Looks like the SD card might be the culprit?

If you're using data on it for apps, quite possibly. Put in a PC USB reader and run CrystalDiskMark or AS-SSD (CrystalDiskMark let's you choose pretty small tests sets, like 50MB and 100MB, which are fine for SD cards). Heck, just test plain 4K, and leave the rest alone. If it doesn't return a few hundred KB/s, it's not fast enough for anything but music/movies.

To compare, my run of the mill Sandisk 32GB SDXC gets 1.5MB/s in CDM's 4K test, as does my phone's Sandisk Ultra 64GB (it was cheaper than the non-Ultra at the time), and a more recent Samsung 16GB gets 2.2MB/s. 0.5MB/s is around 120 IOPS, and is comparable to a typical 5400 RPM HDD. Some no-names still show up not able to do but single-digit IOPS, which just won't work for anything but photos.

 

[Turbonium]

The Pro will be faster. Aside form that, I can't say I have any clue, since the main differences, aside from that, are long-term retention, that shouldn't matter.

The following post seems to imply that TLC NAND is somehow less reliable than MLC NAND (unless it was only a reference to the expected number of cycles):

I even have reservations booting an OS off of a USB stick, at least with any stick using TLC memory.

Also, please give an example of the following:

In general, all SD cards are crap, if you don't get the biggest baddest fastest card out there, compared to other storage.

Are you thinking along the lines of SLC NAND?

 

[hojnikb]

The following post seems to imply that TLC NAND is somehow less reliable than MLC NAND (unless it was only a reference to the expected number of cycles):

It is. TLC is denser (ie. takes more bits per cell) than MLC, so it will be less reliable at the same process node as it has less tolerances for voltage drift (remember, tlc has to distinguish 8 states, while mlc only 4).

 

[hojnikb]

I'm more concerned about my phone freezing, locking-up, and having other issues again when accessing files on a card.

This could either be a crappy card reader, very low IOPS on write (some cards dip as low as 0.01MB/s) or some wierd software glitch.

 

[Turbonium]

It is. TLC is denser (ie. takes more bits per cell) than MLC, so it will be less reliable at the same process node as it has less tolerances for voltage drift (remember, tlc has to distinguish 8 states, while mlc only 4).

Alright, so based on this alone, MLC is inherently more reliable (as defined in my original post) than TLC, assuming all other things being equal.

I mean, it may not even be statistically significant, but I'd expect there to be a definite difference, based on what you said alone.

This could either be a crappy card reader, very low IOPS on write (some cards dip as low as 0.01MB/s) or some wierd software glitch.

I had virtually no issues, ever, accessing large MP4 files (including seeking different points throughout the file, in quick succession), yet I had issues with MP3 files (accessing certain files would lock-up the phone from anywhere from a few seconds, to several minutes; also, some MP3 files would always lock-up the phone at the same point during playback).

I think the reader (phone) was/is fine, but both cards were at fault (bad sectors or otherwise).

 

[Cerb]

Are you thinking along the lines of SLC NAND?

Nothing to do with the NAND. Everything to do with a generally cut-throat market, that has only a small handful of companies able to use their brand names to make real profit margins, and even then only on a small amount of the products, and not much incentive to provide long-lasting products. Since most consumers will not, can not, or don't have knowledge that may empower them to, tell what's better, or require better, SD tends to be a crapshoot, in terms of quality/reliability.

 

[Turbonium]

Nothing to do with the NAND. Everything to do with a generally cut-throat market, that has only a small handful of companies able to use their brand names to make real profit margins, and even then only on a small amount of the products, and not much incentive to provide long-lasting products. Since most consumers will not, can not, or don't have knowledge that may empower them to, tell what's better, or require better, SD tends to be a crapshoot, in terms of quality/reliability.

Yea, I understand that. I just meant that whatever SD cards based on SLC NAND that are out out there might have better quality control, given their target market (also, the price alone). I figured you were saying the same thing with that line I quoted.

 

[VirtualLarry]

Yea, I understand that. I just meant that whatever SD cards based on SLC NAND that are out out there might have better quality control, given their target market (also, the price alone). I figured you were saying the same thing with that line I quoted.

I don't think that there are any SLC SD cards. At least, not for the consumer market. (Perhaps industrial?) TBH, I think that you would be really lucky to find an MLC SD card, at this point.