max micro SD size
Sparkfun and Adafruit both report that the new Ethernet Shield works with SdFat library. Check out the ladyada tutorial
. I note that the tutorial uses half speed on the Arduino SPI bus. I have not found that necessary for my designs. (See Footnote.)
I don't have the new Ethernet Shield, but I am using the SdFat library with SD and SDHC cards up to and including 8 GByte. I haven't tried anything larger, since I don't have anything larger and I haven't had an excuse (or the discretionary funds) to buy anything larger.
I can create files with the Arduino and read/write/modify them on my PC systems (Windows and Linux). I can create files on the PC and read/write/modify them on the Arduino. (SdFat is limited to 8x3 file names, which is no big deal for me.)
The cards that I use come formatted as FAT32, and that's the way I use them. I can't think of a single reason that I would want to reformat them to use FAT16 with any of my systems. If your cards are formatted with a FAT16 file system, you can use them, just the way they come, with SdFat library with no modifications to the library.
Bottom line: I haven't found anything that doesn't work with the SdFat library, and I have never had to reformat an SD card to something other than what it came with. I'm a big fan of SdFat.
I don't know whether the Ethernet Shield will work at Arduino's full SPI port speed or not, and I would like to hear from someone who has tried it. My designs use logic device level shifter circuitry rather than the resistive voltage dividers used on the Official Arduino Ethernet Shield that you get from sparkfun or adafruit or other vendors. I have never seen an error on my systems with the SPI port at full Arduino speed.
I am not an expert on all things SD, but I have read that later versions of the SD cards (the SDHC family) are somewhat sensitive to slow rise and fall times on the input signals. Just a thought. Maybe my concerns about the resistive level shifters are unfounded.
For simple data logging applications, I'm guessing that half speed is adequate. The full speed SPI port gives me a couple of hundred KBytes/sec read speeds and write speeds, and, even at SPI port half speed, I'm thinking that will keep up with Ethernet speeds that you get with an Arduino system.
Or, as my namesake ancestor, DaveFarragut might have said:
amn the Resistors. Half speed ahead!"