microSD card performance comparison

[Andrew2]

However, in my opinion many members of this community come here for reasonably simple answers.

This is what I try to provide. Users should learn 3 things regarding SD cards:

• random I/O is more important than sequential speed, so if you want to buy a new card choose one that shines here. The speed class won't tell you anything in this regard therefore choose any of the 5 top performers from the aforementioned 2 benchmark comparisons
  
• fake SD cards exist and are a real problem (less capacity, less performance, less realiability), you get them even from 'quality retailers' so test your card immediately. Speed results that are published somewhere for a card that is labeled as yours do not matter since you have to check yourself if you got a fake card or not to be able to get a refund and buy a good one instead
  
• Use this simple tool to check your card (for most users this might be H2testw running on their Windows machine before they start writing an image to the card and while H2testw won't tell you anything about random I/O it shows sequential speeds which is enough to identify fakes as well)
  

 (you might notice that this is still the same I said in my first post in this thread)

BTW: If you look at the numbers from Jeff Geerling we rely on... they're also wrong! He never exceeds 18.5 MB/s for sequential speeds which is an indication that something's wrong with his settings, most probably using ondemand scheduler without approriate I/O settings. Since the specific SDIO implementation of both RPi and Pine64 is limited to ~22MB/s:

Code:

root@RPi2:/sys/devices/system/cpu/cpu0/cpufreq# hdparm -t /dev/mmcblk0

/dev/mmcblk0:
Timing buffered disk reads:  66 MB in  3.02 seconds =  21.84 MB/sec

Small ARM boards behave differently than x86 PCs and wrong CPU settings also affect I/O performance. Do your users know that when submitting results? Some basics: http://linux-sunxi.org/SATA#Performance

So in fact your users are testing different cpufreq governors combined with different settings (might make a difference of up to 5-6 MB/s when testing sequential speeds), different I/O schedulers and different IRQ distribution settings but think they test their cards. There will be OS images that take care of the aforementioned stuff (thinking of Armbian when available sometimes) and there will be some that don't and might use settings that lead to killed CPU cores due to overheating before (then performance will even drop lower and submitted results are even more meaningless).

So while even Jeff Geerling's numbers aren't measured correctly these numbers have a value unlike the ones from the spreadsheet you try to fill here. Since we can assume that he tested all the cards with nearly identical settings and the only purpose of his list is to identify the 5 top performers regarding random I/O (and for this purpose his and the other list are pretty useable).

So please feel free to ignore any of the aforementioned background information and collect further numbers without meaning. But please refrain from telling users they should rely on any of these numbers for buying decisions or draw conclusions from a table row they found on docs.google.com containing the string 'SanDisk Extreme Pro' for a card they own where 'SanDisk Extreme Pro' is written on. Since it's not possible, there is NO relation between the performance of their device in question and the results someone else wrote in a spreadsheet row sometimes before.