Identifying counterfeit microSD cards on a Beaglebone Black

[Dr. Rolf Jansen]

Am 18.03.2017 um 12:30 schrieb Warner Losh <imp at bsdimp.com>:
> On Sat, Mar 18, 2017 at 8:44 AM, Dr. Rolf Jansen <rj at obsigna.com> wrote:
>> I bought a 16 GB microSDHC SanDisk chip rated at 4 MB/s write speed for use with my Beaglebone Black.
>> 
>> The internal flash offers practical write speeds in the range of 2 to 3 MB/s when copying data to it from a NFSv4 volume depending on the size of the files being copied. Executing the same copy operation with said microSDHC card as the target I see only 0.1 to 0.2 MB/s (less than 1/10).
>> 
>> I suspect now that I got a counterfeited card. Before I dump it, I would like to run a definitive non-destructive test, preferably on the Beaglebone Black, and I would like to ask you for suggestions.
>> 
>> Also, it would be nice to see some speed values as a reference for microSDHC card write speeds on:
>> 
>>    FreeBSD 12.0-CURRENT (BEAGLEBONE) #0 r315413
>> 
>> Many thanks in advance for any help.
> 
> Copy a huge file from /dev/zero. Smaller files in the filesystem
> generate a lot of overhead and 'wait points' that slow down overall
> performance.
> 
> Or better yet, dd to the raw device. /dev/random should generate data
> faster than the card can handle. Depends on what you mean by
> 'non-destructive'
> 
> And all NAND sucks. It's a pig with lipstick on it. So you won't get
> even performance if the FTL in the SD card sucks. Garbage collection,
> internal house keeping, etc all can steal performance from the user
> application. These cards are generally designed to take a burst of
> writes when the camera or video is taken, then have it read back
> later. A mixed workload was never optimized for on most of these
> cards, so it can also significantly degrade performance even at low
> percentage mixtures.
> 
> So all those things could be going on w/o it being a counterfeit. :(.
> Of course, it could have all those things going on and also be a
> counterfeit. Hard to say for sure unless the performance is wildly
> different. But 4MB/s write performance is pretty pathetic for a card
> of that size, so it's on the low end, which suffers most from uneven
> performance and "down hill with the wind" spec numbers.

Warner, thank you very much for taking your time responding.

It is a Class 4 card, i.e. guaranteed minimum write speed should be 4 MB/s, and I know the difference between advertised and practical speed, I would have expected at lest 50 % of the advertised speed, i.e. something in the range that can be achieved with the internal flash of the BBB. I would even be happy if it would come close to 1 MB/s. But 0.1 MB/s that is a quit huge difference -- 40 times less than the advertised speed.

You said, that 4 MB/s is "pretty pathetic". Therefore let me ask a different question. What is the best write speed that can be achieved with what model of a microSD card on a Beaglebone Black running FreeBSD 12-Current?

Many thanks and best regards

Rolf