My initial research has not been successful, so now to the experts!
I have an external 1TB USB2.0 drive formatted as a single partition EXT4 drive. It has worked fine for a long time and has not caused any problems. But, I recently purchased a PogoPlug (a small network server that uses an user-provided USB drive). The Pogo works fine with all my other FAT32, NTFS, and EXT2/3 drives. But, the PogoPlug does not support EXT4 (vendor refuses to provide a solution). I don't currently have a sufficiently large other drive to copy the EXT4 drive to save its contents and reformat the EXT4 to EXT3.
Does anyone have a suggestion to converting a EXT4 drive to EXT3 without losing the contents?