Automatic migration from internal to external?

Hi, have had aTV Flash for a while now, all working lovely but now I would like to move all the data sat on the ATV onto my External USB disk & not use the disk on the ATV at all, if I switch aTV Flash to external storage mode will it automatically migrate everything to the external disk or will I have to move it manually using an ftp client?

If you follow the guide at the link below for setting up a USB drive as primary storage all synced iTunes media will be automatically transferred to the external drive. Any media you transferred manually via FTP must be manually moved to the external drive.

Thanks for the info, I did read that before but wondered if there was a way to do it without erasing the external disk first (as I already have been using that for content as well but wanted to consolidate everything onto the single drive), looks like I will just have to manually move them via ftp.