@zeke : SD cards are rated for 3.3V (1.8V for some - with 3.3V init), 5V will kill them?
Lately I have accessed cards via FatFS on MSP432E401Y and TM4C1294 LaunchPads with power supplied from the BoosterPack header without problems.
Up to 500mA can be supplied via the LDO on the MSP432P401R LaunchPad, and I believe enough is left for a SD card (draw is typ. 20-100mA according to wikipedia).
The code I used was from the TI SDKs.
Maybe I am thinking of the PetiteFS way of using an SD card but doesn't that SD card need to be first formatted on a PC and have a file created as well?
Then, the MSP430 would access the SD card, open up the pre-existing file, and then write to it?
I would verify the SD card on a PC first by formatting it then creating an empty text file on it. Then, get the MSP430 to see it then open it.
Double check the wiring of the card.
And make sure that you have a really good +5V power source for that SD card. I have read that they want a bunch of current to operate properly. And, I suspect the dev board cannot supply that much current on the +5V line. Gotta verify that too.