Date: Sat, 18 Mar 2017 09:30:15 -0600 From: Warner Losh <imp@bsdimp.com> To: "Dr. Rolf Jansen" <rj@obsigna.com> Cc: "freebsd-arm@freebsd.org" <freebsd-arm@freebsd.org> Subject: Re: Identifying counterfeit microSD cards on a Beaglebone Black Message-ID: <CANCZdfo97-iFg4zLxbyQhv9rPrd8eU5rN-mzDL5wz3xj6XxrsQ@mail.gmail.com> In-Reply-To: <D08E6528-56E6-4229-8722-D87116B8064D@obsigna.com> References: <D08E6528-56E6-4229-8722-D87116B8064D@obsigna.com>
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On Sat, Mar 18, 2017 at 8:44 AM, Dr. Rolf Jansen <rj@obsigna.com> wrote: > I bought a 16 GB microSDHC SanDisk chip rated at 4 MB/s write speed for u= se with my Beaglebone Black. > > The internal flash offers practical write speeds in the range of 2 to 3 M= B/s when copying data to it from a NFSv4 volume depending on the size of th= e 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 microS= DHC 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
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