Archive for July, 2013

SD Card Benchmark on a Raspberry Pi

Posted by smoreau in Linux on 01 Jul 2013

Some time ago, I bought a Raspberry Pi. I am not going to describe what it is here, but you can read more about it on this page.

The first thing you need to buy when you’ve got a Raspberry Pi is a SD card. But the question I asked myself is: “Which one?”. Indeed, there are so many models with different type, capacity and speed. 🙁

I first checked the compatibility list found on the Embedded Linux Wiki:
http://elinux.org/RPi_SD_cards#Working_.2F_Non-working_SD_cards
But this list didn’t help me much. Indeed, out of them, which one should I buy?

This is why I decided to test two SD cards with two different speed:

  • SanDisk SDSDXPA-008G-X46 8GB 95MB/S Extreme Pro SDHC Class10
  • SanDisk SDSDX-032G-FFP 32GB 45MB/S Extreme SDHC Class10

As you can see, the speed of the first one is 95MB/S against 45MB/S for the second one. Does it mean the Raspberry Pi will run twice quicker?
Let’s check it by benchmarking the cards.

I used IOzone to benchmark these cards. Unfortunately, IOzone is not available for ARM on ArchLinux. I wrote a separate article about it.

I ran the exact same command for both cards:

iozone -e -I -a -s 50M -r 4k -r 512k -r 16M -i 0 -i 1 -i 2

Please find below the result for the SD card with a speed of 95MB/S:

                                                    random  random    bkwd   record   stride                                   
      KB  reclen   write rewrite    read    reread    read   write    read  rewrite     read   fwrite frewrite   fread  freread
   51200       4    1422    1502     5841     5838    5688     878                                                          
   51200     512   20743   20924    22094    22130   22121    8313                                                          
   51200   16384   20090   21349    22413    22514   22458   21351

The full output can be found here.

And the following is the result for the SD card with a speed of 45MB/S:

                                                    random  random    bkwd   record   stride                                   
      KB  reclen   write rewrite    read    reread    read   write    read  rewrite     read   fwrite frewrite   fread  freread
   51200       4    1653    1858     4566     4716    3996     755                                                          
   51200     512   20515   19534    21953    22031   21867    4722                                                          
   51200   16384   15841   21240    22311    22390   22384   21177

The full output can be found here.

So, it looks like the difference is not that big. Indeed, the SD card with a speed of 95MB/S is not twice quicker than the other one. Why is that? In my opinion, this is directly linked to the actual speed of the SD card reader within the Raspberry Pi.
Which means that it doesn’t matter which card you are using, you won’t go further than 22MB/S anyway.

Finally, please find below some other benchmarks on the same topic:

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