The new Teensy 3.6 has an on-board microSD connected to a fast 4-bit wide SDIO bus.
Here are first SdFat performance results for various multi-block writes and reads.
The first column is read/write size, the second is write speed in KB/sec, and the third is read speed in KB/sec.
Teensy 3.6
size, write, read
bytes, KB/sec, KB/sec
512, 601.82, 2221.44
1024, 1151.74, 3214.67
2048, 2177.06, 5098.84
4096, 3739.32, 7984.80
8192, 4188.10, 9313.15
16384,7359.31, 13330.17
32768, 12381.25, 15125.21
Write at 12.3 MB/sec and read at 15.1 MB/sec with 32KB transfers!
I hope to improve this by implementing a SdFatEX style driver. I expect much faster small transfers.
Uno vs Teensy 3.6, RAM 2 KB vs 256 KB, flash 16 KB vs 1024 KB, and F_CPU 16 MHz vs 180 MHz.
Sketch uses 35,032 bytes (3%) of program storage space. Maximum is 1,048,576 bytes.
Global variables use 39,092 bytes (14%) of dynamic memory, leaving 223,052 bytes for local variables. Maximum is 262,144 bytes.