I'm not sure why you would want to backup to a network HD in your house. You probably have your reasons, but usually the upstream bandwidth at home is quite limited which would horribly slow down the restore process. Instead I would suggest backing up to some cloud storage provider that can provide decent bandwidth in- and outgoing and redundancy as well.
I use Jungle Disk Server Edition to backup several Linux production servers. It's very affordable and has worked well. You'd set a pre-backup script to dump the MySQL db's and set Jungle Disk to backup the dumpfiles, and images. Jungle Disk de-duplicates, compresses and encrypts the data before uploading.
Jungle Disk can upload to Rackspace Cloudfiles and to Amazon S3, so your choice which storage service you prefer. There's a cross-platform application to remote control the backup services.