4 years ago
JP> Do not move the goal posts.
Sorry but you did. We are talking about both read and write speeds. They both matter when making backups and copies.
JP> First, to MAKE a backup you need to read the card.
Yes and second you have to write to another device, mostly an SDcard, not device Zero ;-).
JP> That read happens (if things are done right) much more often than a JP> 'restore'
May be at your site, but not here.
JP> where you write the backup back to the card.. JP> The restore may even never happen if things are done right.
For your own operated cards yes. But I am creating SDcards for skippers who buy a Raspberry Pi 3B(+) for AIS+ECDIS inland navigation, so for me the write time used counts very much too! In that way the right command used is essential.
JP> On the write timing issue, it will very likely just be limited by he JP> specified card write speed, JP> if it is a half way decent card it will take care of the allocation.
As I showed this day with the 32 GB copying, the right commands counts very much.
JP> Well, I recently bought let me see, JP> MB-MC32DA/EU Samsung Evo+ 32 GB Micro SD class 10 met adapter JP> That was in March, is used in my drone, and in my video camera. JP> read speed up to 80 MB/sec. JP> write speed up top 20 MB/sec.. JP> UHS-I-speed class 1 (U1), class 10 JP> JP> sd-adapter/MB-MC32DAEU/ JP> Best ones I could find.
I think my Kingston 16, 32 and 64 GB versions have the same specifications. I paid E.7.95, E.9,95 and E.19,95 for them. So the 16 GB one is relatively more expensive than the 32 and 64 GB ones. in Doorwerth.Gld.NL.
JP> I have some older 8 GB and 16 GB cards in the raspis, JP> but I am sure as I just went for the best in those days JP> that those have a decent control chip.
Some friends of my lost cards by using thim intensively. The answer is to not fill them up for more than 50%. That way the card software can level the wear better. Make a ramdisc and use that for scrap, as I did for RISC OS at the Pi. I now have to figure out how to make a ramdisc under Raspbian Stretch Linux, and move the scrapfiles to after booting, for less wear. Electronic storage at SDcards, USBsticks and SSD HDD's have shorter lifetimes than magnetic media had, so beware.
JP> Also have a bunch (from ebay) 2 GB cards for things that do not JP> support > 2 GB, or do not need that and the speed, JP> such as auto-pilot drone: JP> JP> old WiFi webserver, etc.
The only apparatus with a 2 GB limit are my Acorn RiscPC and the Aldi Traveler DC8600 still photocamera.
JP> And of course I wrote the software to read / write to some of those JP> cards myself in asm actually JP> All sector based... :-)
Assembler was a bridge to far for me.
JP> You can use hdparm to get some info on the cards you have. JP> Not sure you can still get older cards, the old 2 GB ones I got from JP> ebay ware almost more expensive JP> than the new fast ones.. getting rare for people who do not want to dump JP> old equipment, sellers can ask what they want, like for antiques :-)
I remarked the same attitude. So I gathered some old 2GB cards from friends who didnot use them anymore. I takes more tha a year to fill up the 2 GB card with the photocamera. I made more than 6600 photo's since 2006, and I am using now the 7th SDcard in that camera.
JP> But next time I need to write back a raspi backup image (hope it never JP> happens) I will show the write timings with - and without bs=1M.
W'll see that in future I hope.