On Tuesday 08 May 2012, Michael Hudson-Doyle wrote:
On Tue, 8 May 2012 16:30:05 +0300, Riku Voipio riku.voipio@linaro.org wrote:
I think following any SD card brand for quality is a losing proposition. Every brand sources chips wherever they cheapest get, and thus what is inside the package changes from one batch to another. Everyone has anecdotal evidence of one brands memory cards failing more often than another, but nobody has solid statistics...
I disagree. We've learned a lot about the various brands and what they do by now. We know that Sandisk consistently has good controllers (unless you end up with a fake one that can be detected by looking into the ID registers) and that it has enabled them to use cheaper flash chips than most others. I'm rather certain that the companies who make their own controllers and flash chips (sandisk, samsung, lexar/micron) actually use their own chips all the time, while most others take whatever they can get their hands on. We also know that Kingston has uses Toshiba controllers with a horribly bad GC algorithm and I suspect that they have to make up for this by using better (MLC instead of TLC) flash chips (which means they are good for video cameras but not for Linux).
We also know that Samsung has caught up recently and is now making excellent controllers even for their "essential" series cards -- these behave much better than anything else I've tested before (except eMMC and actual SSD drives).
Finally, we have ways to test the erase block size and type (SLC/MLC/TLC) in order to determine whether the cards are any good. TLC is generally not very reliable and any erase block size larger than 4MB will cause too much write amplification according to our simulation, so random write performance and longevity suffer.
I guess you're right, depressingly enough. In any case I bought a couple of sandisk microsdhc cards, one batch of which appears to have been quite reliable in the lab...
Yes, that seems to be a good choice. I've never encountered a Sandisk "ultra" or "extreme" card that wasn't really good. Their cheaper class 2 or class 4 cards are much less trustworthy IMHO because they use TLC memory.
Arnd