Date: Sat, 18 Mar 2017 15:03:38 -0300 From: "Dr. Rolf Jansen" <rj@obsigna.com> To: freebsd-arm@freebsd.org Subject: Re: Identifying counterfeit microSD cards on a Beaglebone Black Message-ID: <A633D336-2581-4C51-A3C9-7AFD0ABB9E9F@obsigna.com> In-Reply-To: <CANCZdfo97-iFg4zLxbyQhv9rPrd8eU5rN-mzDL5wz3xj6XxrsQ@mail.gmail.com> References: <D08E6528-56E6-4229-8722-D87116B8064D@obsigna.com> <CANCZdfo97-iFg4zLxbyQhv9rPrd8eU5rN-mzDL5wz3xj6XxrsQ@mail.gmail.com>
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Am 18.03.2017 um 12:30 schrieb Warner Losh <imp@bsdimp.com>: > 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 use with my Beaglebone Black. >>=20 >> 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). >>=20 >> 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. >>=20 >> Also, it would be nice to see some speed values as a reference for = microSDHC card write speeds on: >>=20 >> FreeBSD 12.0-CURRENT (BEAGLEBONE) #0 r315413 >>=20 >> Many thanks in advance for any help. >=20 > 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. >=20 > 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' >=20 > 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. >=20 > 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
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