I'm working on a data logger for a small project that will be subject to very harsh loading conditions (high G, high T, etc.). For storing the logged data, I've deliberated between running two DataFlash chips or just running two SD cards, both off of a shared SPI bus and both storing identical information for redundancy.
The question I have is, what's the best way to do this? I was thinking about tying the SCLK, MISO, and MOSI lines together with independent CS lines, and then for a writing operation bringing both CS lines low to select both cards/chips. That way, both devices would be writing the same data at the same time, but I worry about the two chips fighting with each other.
The advantage to SD over DataFlash is that I can easily remove the cards, pop them in a computer, and read the data. The disadvantage is that I worry about the stability of the SD card under high loading. I don't want the cards shifting around or otherwise coming out of the slot (or breaking connection).
Really, the only advantage that the DataFlash chips have is that they're surface mount, solid state devices. If the reflow is done properly, I really don't have to worry about the chips coming off, breaking, etc. The big disadvantage to them is writing code and building a circuit to interface with them once the data has been logged (in order to pull the data off with the computer). The SD cards don't have that problem...
Any recommendations you all have would be most appreciated. Thanks!