https://github.com/greiman/SdFat-beta

sdfat.ino

#include "SdFat.h"
// SPI_DRIVER_SELECT == 0 // Must be set in SdFat/SdFatConfig.h

#define PIN_SD_CS 33
#define PIN_SD_MOSI 27
#define PIN_SD_MISO 25
#define PIN_SD_SCK 26

#define SD_FAT_TYPE 0
SPIClass spi(HSPI);
//#define ENABLE_DEDICATED_SPI 1
#define SD_CONFIG SdSpiConfig(PIN_SD_CS, DEDICATED_SPI, SD_SCK_MHZ(25), &spi)

SdFat sd;
SdFile file;

void setup()
{
    Serial.begin(115200);
    softSpi.begin(PIN_SD_SCK, PIN_SD_MISO, PIN_SD_MOSI, PIN_SD_CS);
    // Wait for USB Serial
    while (!Serial)
    {
        yield();
    }
    Serial.println("Type any character to start");
    while (!Serial.available())
    {
        yield();
    }

    if (!sd.begin(SD_CONFIG))
    {
        sd.initErrorHalt();
    }
    Serial.println(F("Start."));
    uint8_t *buf = (uint8_t *)malloc(16384);
    for(int i=0;i<16384;i++)
    {
        buf[i] = i&0xff;
    }
    long t = micros();
    if (!file.open("SoftSPI.txt", O_RDWR | O_CREAT))
    {
        sd.errorHalt(F("open failed"));
    }
    for (int i = 0; i < 32; i++)
    {
        file.write(buf, 16384);
    }
    file.close();

    Serial.printf("Done:%d\n", micros()-t);
}
//------------------------------------------------------------------------------
void loop() {}