I've lately purchased a Synology DS212j and I intended to use my two 3.5" HDs into it. One of them was in used as an external HD. Thus when I install these two unit in NAS, it asked me to formatted in order to used with its format (I think it's ext3?) . I installed the Disks and omit the formatting option.

I just got another 3.5" Hard Disk now. I've installed it in the NAS. everything's fine. However, when I take out the (used) HD from the NAS and install back in the standalone casing, I found out that it can't be read from both OSX an Windows 7. I've tried with ext2sd and I only found 2GB portion of the whole 1.5 TB Hard Disk.

Here's another reference from EASEUS Partition Master