Quoting Gene Heskett (2019-09-18 18:20:43) > On Wednesday 18 September 2019 11:36:41 John Hasler wrote: > > > Jonas writes: > > > Please demonstrate just one single example of dd being faster than > > > cp to transfer a full raw image to a raw device! > > > > On modern systems you would probably need to be doing terabyte > > transfers between disks on the same machine. Back in the days when > > a megabyte was a lot dd was *much* faster. > > > > On an SD card I think that the write speed of the card is probably > > the limiting factor. > > It is, and the makers lie a lot, taking advantage of the buffering to > get thier 100 MBs rating for small writes. For gigabyte transfers I > often see sub 20 MB/S toward the end. But you may want to steer clear > of the 64GB+ cards, exfat is creeping into the sdhc arena, and I > either have a defective NEW PNY 64GB, or this stretch install can't > touch it because its exfat. I bought 2 recently, same exact part > number, slightly different card gfx, the 85 meg rated one doesn't > mention exfat, works, the 100 MB/S rated one mentions exfat and is > untouchable.
Regarding quality of SD cards, I trust advices from Thomas Kaiser. Here's his advice on which brands to trust: > Only a few vendors on this planet run NAND flash memory fabs, only a > few companies produce flash memory controllers and have the necessary > know-how in house. And only a few combine their own NAND flash with > their own controllers to their own retail products. That's the simple > reason why at least I only buy SD cards from these 4 brands: Samsung, > SanDisk, Toshiba, Transcend Above quote is from https://forum.armbian.com/topic/954-sd-card-performance/page/3/?tab=comments#comment-49811 which is linked from front page intro to that thread - as part of this more general advice + warning not to waste time reading the whole thread: > Warning: This whole thread is only about historical information now > since it's 2018 and we can buy inexpensive and great performing A1 > rated SD cards in the meantime. Buying anything else is a mistake so > directly jump to the end of the thread for performance numbers and > recommendations. On a related note, here's Kaiser's more detailed notes on A1/A2 rating: https://github.com/ThomasKaiser/Knowledge/blob/master/articles/A1_and_A2_rated_SD_cards.md - Jonas -- * Jonas Smedegaard - idealist & Internet-arkitekt * Tlf.: +45 40843136 Website: http://dr.jones.dk/ [x] quote me freely [ ] ask before reusing [ ] keep private
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