It's theoretically possible but I'm afraid of operation failure for such complex array. So It's nice to have simple user interface like Synology.
You can also replicate Dropbox quite trivially by getting an FTP account, mounting it locally with curlftpfs, then use SVN or CVS on the mounted filesystem [1]
You can do this yourself with ease by creating 2TB partitions on all drives and setting up RAID separately on each. Then you could use LVM to access them as unified storage, or keep them separate for extra flexibility when restoring.