Good advice from DigiGal, which isn't suprising.
The DR-2d will reformat, or if it recognizes the existing format structure, will simply ask to write necessary system files.
More detail than you probably want, but here's how I manage SDHC cards so that I can swap them between any of my recorders or a camera as necessary, without reformating or deleting the files that may already be on there until they are near full-
I leave the files on the card after transfering, simply as an extra backup until I have redunant copies on a couple hard drives. Once I've filled a card and need to wipe it clean, I do that by formating it on a one of my windows machines, at which time I give the card a unique file name at the same time to ID and differentiate it from my other cards for easier management. I've written a number on the outside of each card with a sharpie to tag it, so the file name is simply that number and the card's formatted capacity, something like this:
#12_30GB
I then put in in the DR-680 which is the most picky of my recorders about formatting cards to it's liking, and it asks to format it. That formats and writes some necessary files and folders, but retains the card name. I then put it in a DR2d and let it write it's system files. That is not a full format and retains the card name as well as the DR-680 files and folders.
At that point I can swap that card between the DR-680, DR-2d(s), R-44, R-09(s), or a camera. The Edirols aren't picky about formating and write no system files or folders. Like most cameras they will work with any properly computer formatted card.
Like DigiGal suggests, It’s always best to format on the machine you intend to use the card with, but I’ve had no problems doing this. It makes management easier for me and I can throw any of my SDHC cards with free space into any of these devices without worrying about loosing what's already on card.