这里选取了三款TF卡进行测试

《雷龙发展提供的CS创世SD NAND》

1、写的速度：

100+0 records in~# time dd if=/mnt/1.txt of=/dev/null bs=1M count=100 iflag=direc
100+0 records out
104857600 bytes (105 MB, 100 MiB) copied, 4.17846 s, 25.1 MB/s

real    0m4.259s
user    0m0.001s
sys     0m0.658s
ynct@myir-yg2lx:~# time dd if=tempfile of=/mnt/1.txt bs=1M count=100 conv=fdatas
100+0 records in
100+0 records out
104857600 bytes (105 MB, 100 MiB) copied, 4.24326 s, 24.7 MB/s

速度为24.7MB/s
2、读的速度：

root@myir-yg2lx:/# time dd if=/mnt/1.txt of=/dev/null bs=1M count=100 iflag=direct,nonblock
100+0 records in
100+0 records out
104857600 bytes (105 MB, 100 MiB) copied, 1.88799 s, 55.5 MB/s

real    0m1.893s
user    0m0.005s
sys     0m0.062s

读的速度达到了55.5MB/s

ScanDisk 16G

插入SD卡后自动识别：

[ 4205.897770] mmc1: new high speed SDHC card at address ef6d
[ 4205.909758] mmcblk1: mmc1:ef6d AFGCC 14.8 GiB
[ 4205.927461]  mmcblk1: p1 p2 p3

写的速度为24.7MB/s：

100+0 records out# time dd if=/mnt/1.txt of=/dev/null bs=1M count=100 iflag=direc
104857600 bytes (105 MB, 100 MiB) copied, 4.25149 s, 24.7 MB/s

real    0m4.332s
user    0m0.001s

读的速度为40MB/s

100+0 records in~# time dd if=tempfile of=/mnt/1.txt bs=1M count=100 conv=fdatasy
100+0 records out
104857600 bytes (105 MB, 100 MiB) copied, 2.62025 s, 40.0 MB/s

real    0m2.625s
user    0m0.001s
sys     0m0.125s

Gemaixi512G

插入后自动识别

root@myir-yg2lx:~# [ 4363.624406] mmc1: card ef6d removed
[ 4380.805766] mmc1: new high speed SDXC card at address 2143
[ 4380.812127] mmcblk1: mmc1:2143 APPSD 500 GiB
[ 4380.825030] Alternate GPT is invalid, using primary GPT.
[ 4380.830420]  mmcblk1: p1 p2 p3

写入速度24.7MB/s：

[ 4380.8304g2lx:~# time dd if=tempfile of=/mnt/1.txt bs=1M count=100 conv=fdatasync
100+0 records in1.txt of=/dev/null bs=1M count=100 iflag=direc
100+0 records out
104857600 bytes (105 MB, 100 MiB) copied, 4.24071 s, 24.7 MB/s

real    0m4.323s
user    0m0.001s

读取39MB/s：

syst@myir-yg2lx:~# time dd if=/mnt/1.txt of=/dev/null bs=1M count=100 iflag=direct,nonblock
100+0 records in~# time dd if=tempfile of=/mnt/1.txt bs=1M count=100 conv=fdatasy
100+0 records out
104857600 bytes (105 MB, 100 MiB) copied, 2.66665 s, 39.3 MB/s

real    0m2.671s
user    0m0.001s
sys     0m0.130s

终上所述TF卡的写入速度均为24.7MB/s，但是读取的速度还是以SD NAND速度为最快，达到了55.5MB/S。