Date: Fri, 24 Mar 2017 08:45:33 -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: <49570189-CEB5-47BE-966A-BCF7FC73A415@obsigna.com> In-Reply-To: <CANCZdfpe8LhXOYM3j%2B_p150k_z8j_S=AmPnrH-gEtqyh51B1fw@mail.gmail.com> References: <D08E6528-56E6-4229-8722-D87116B8064D@obsigna.com> <CANCZdfo97-iFg4zLxbyQhv9rPrd8eU5rN-mzDL5wz3xj6XxrsQ@mail.gmail.com> <A633D336-2581-4C51-A3C9-7AFD0ABB9E9F@obsigna.com> <1489864043.40576.219.camel@freebsd.org> <16B03E70-00E6-4C17-9A9A-8601F4C07364@obsigna.com> <2F7D5F42-E50A-4761-9EEC-DC873BD7D0AB@obsigna.com> <CAB=2f8wR57ip7gUVGQqHNAzCHq-qiC8nwVG1%2BASu1N3kCcKrEQ@mail.gmail.com> <70C95FC9-4B0A-4DA4-9857-EFAF41522D1B@obsigna.com> <1490281652.58015.71.camel@freebsd.org> <CANCZdfrjngmk8S%2B-Oz-rCUqKW8by4GBrRAxSWivMx-DL0M_LSw@mail.gmail.com> <7E957E90-5579-4A7F-83DC-1B5522833EC2@obsigna.com> <CANCZdfpe8LhXOYM3j%2B_p150k_z8j_S=AmPnrH-gEtqyh51B1fw@mail.gmail.com>
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Am 23.03.2017 um 23:52 schrieb Warner Losh <imp@bsdimp.com>: > On Thu, Mar 23, 2017 at 8:46 PM, Dr. Rolf Jansen <rj@obsigna.com> = wrote: >> Am 23.03.2017 um 17:37 schrieb Warner Losh <imp@bsdimp.com>: >>> On Thu, Mar 23, 2017 at 8:07 AM, Ian Lepore <ian@freebsd.org> wrote: >>>> On Thu, 2017-03-23 at 00:42 -0300, Dr. Rolf Jansen wrote: >>>>> Am 21.03.2017 um 13:25 schrieb Luiz Otavio O Souza = <lists.br@gmail.com>: >>>>>> On 19 March 2017 at 18:45, Dr. Rolf Jansen wrote: >>>>>>>>>>>>=20 >>>>>>>>>>>> ... ask you for suggestions. >>>>>> [picking a random message to reply] >>>>>>=20 >>>>>> I just saw an email from SanDisk support (whatever this means) >>>>>> where >>>>>> they claim the only supported model for this kind of use is the >>>>>> high-endurance series: >>>>>> = https://www.sandisk.com/home/memory-cards/microsd-cards/high-endura >>>>>> nce-microsd >>>>>>=20 >>>>>> This same email says that running any kind of OS in any of the >>>>>> other >>>>>> card models automatically breaks the warranty. >>>>> Luiz, thank you very much for the note. Do you know, whether this >>>>> high endurance XC card is compatible with the Beaglebone Black? >>>>=20 >>>> I would assume that it is, they're typically just standard sd cards >>>> with flash arrays based on SLC technology and with a lot of extra = space >>>> for reassigning bad blocks (a card that claims 8gb capacity could >>>> actually have 4x that many blocks or more available internally). >>>=20 >>> I don't think there's 4x over-provisioning. Where do you get that = figure? >>>=20 >>> When I was at Fusion I/O, the designs there were all in the 9-24% >>> range, and our "intel" on what others were doing showed a range of = 5% >>> to 40% depending on the market segment and type of NAND use. If they >>> are really using SLC NAND for these cards, the sparing is likely = less >>> because TLC NAND has about a 200-300 endurance rating (program erase >>> cycles per erase block). MLC is between 3000-5000. SLC is like >>> 30,000-100,000. SLC has also 10-100x better error rates than MLC = which >>> has 10-100x better than TLC due to how the charge nodes are = programmed >>> and the tolerances associated with that programming. There was >>> constant pressure to come up with designs that needed less sparing, = so >>> I doubt things have changed to require 4x over provisioning.... What >>> might be going on when people say that has to due with a feature of >>> modern NAND chips: they can be programmed as SLC, MLC or TLC often = on >>> a per-erase block basis. In that case, a SLC configuration with a = 33% >>> over provisioning would have a 4x maximum theoretical raw capacity >>> over the selected size for the drive (so a 8GB drive would have 8GB = * >>> 1.33 (over provisioning: spares and OOB) * 3 (TLC multiplier) or = 32GB >>> of raw capacity). >>>=20 >>>> But be aware that high-endurance or industrial-rated cards can be = very >>>> expensive. I think at work we pay around $40 each for = industrial-rated >>>> 8gb cards. (One of them was included in those test results I = posted, >>>> and the performance was among the best, at least you get something = for >>>> all that extra money.) >>>=20 >>> Part of the issue is that NAND chips these days can be SLC, MLC or = TLC >>> depending on how you program them (often on an erase-block = level).[*] >>> This means that the 8GB SLC card could also be a 16GB MLC card or a >>> 24GB TLC card (well, due to sparing it likely wouldn't scale >>> linearly). So from that perspective, I can see where a 4x number = might >>> come up (high number of bits possible for the die vs capacity >>> configured for SLC + spares). At 33% sparing, the differences = between >>> the SD presented capacity point of 8GB would have close to 32GB of >>> potential raw capacity were it run in TLC mode.... In addition, high >>> endurance cards are often selected from the wafers at manufacturing >>> time because they have the lowest error rate and other metrics so = the >>> NAND makers know that they will survive (the NAND manufacturing >>> process isn't too uniform across the wafer due to micro variations = in >>> the wafer and other effects at the nano-scale). Often times these = are >>> also pulled from processes that typically yield better results but = are >>> more expensive. So the relative rarity of the raw dies plus the >>> increased production cost plus running them in a faster, more = reliable >>> mode all lead to the cards being more expensive.... >>>=20 >>> So that's why it's so expensive, especially on the high end: you are >>> paying extra for quality. >>=20 >> Warner and Ian, thank you very much for sharing your much deeper = insights on the matter. >>=20 >> I am setting up a prototype for a mostly autonomous measurement = device for an industrial application using the BBB as the controller. = For this reason I am interested in the ti_adc driver, and I was glad = that I got it working. >>=20 >> Once the device has been setup, writes to the SD card will be limited = to logging measurement data and activity events besides the normal = FreeBSD logging. The 4 GB internal flash of the BBB would be more than = sufficient to hold everything, however, I was thinking that using an = external SD card in order not to damage the BBB because of flash wear, = would be a good idea. >>=20 >> Well, for this kind of application $40 is still in the budget, = however, it comes already close to the cost of the BBB itself. Perhaps, = I simply forget the SD cards and provide to my future customers spare = BBB's. >>=20 >> Anyway, I guess I need to do some lifetime simulation of the external = flash compared to the internal one, so I could take a more educated = decision based on these results. >=20 > Lifetime / endurance is normally normalized to 'Drive Writes Per Day'. > You should check to see what the endurance of the eMMC in the unit is. > You may have enough headroom to just log there. SSDs always specify > this, but SD cards seem to rarely do. I did a search on these figures for the BBB, although I did not found = the exact value, what I read was discouraging enough for me. So I = decided not to touch the internal flash too much. Many thanks again Rolf=
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