On Tuesday 08 May 2012, Michael Hudson-Doyle wrote:
> On Tue, 8 May 2012 16:30:05 +0300, Riku Voipio <riku.voi...@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
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