• microsd-cards comparison 2018 comparison 2019

dnf -y install hdparm

wget https://www.iozone.org/src/current/iozone3_489.tar
tar xvf iozone3_489.tar
cd iozone3_489/src/current
make -j5 linux-arm
./iozone -e -I -a -s 100M \
    -r 4k -r 16k -r 512k -r 1024k -r 16384k \
    -i 0 -i 1 -i 2

• size/serial:
  • udevadm info -a -n /dev/mmcblk0|egrep '{size}|serial|date|name'
  • To find out size, and serial for identification
• read seq:
  • dd if=/dev/mmcblk0 of=/dev/zero bs=1M count=512
  • To measure sequential read speed
  • Similiar to hdparm -t /dev/mmcblk0
• rreads/rwrites:
  • iozone -e -I -a -s 100M -r 4k -r 16k -r 512k -r 16384k -i 0 -i 1 -i 2
  • random read/writes, 4kbyte chunks and 512byte chunks

• 16G/0x47181309, Fedora32 for Raspi4, Toshiba
• 16G/0x000001ed LAZOS, Raspbian
• 32G/0x00000015 LAZOS, mp3s
• 32G/0x28ca8ad8 Toshiba, 02/2018, Nintendo switch L4t/Fedora32
• 32G/0x7cc4f718 ELECOM MF-BMSD-032, 01/2020, 2000円
• 32G/070003F3E21C4C65 ELECOM (USBstick), 2000, 2170円

• USB3 flash is connected with >100MB/sec, and sdcards limited to ~40MB/sec on the Raspi4.
• USB3 flash sticks can be as slow as sdcards for random access.
• Profiling typical OS operations, I see many 4kb and 8kb accesses, cards are quite bad at that, they are optimized for sequential access.
• Cards can be profiled with one reader, and have a comparable profile on other readers. Capping bandwidth wise applies of course, the reader itself can be the bottleneck.