warpcafe wrote:very intersting topic. By the way, IBM's DualStor also was my preferred backup solution (some years ago) because it was very easy to use and "nice". The bad thing was that (back in that time) it was already hard to find suitable tape drives (or suited drivers)...
I used to use DualStor with an old Conner floppy-controller-connected tape drive. When I decided I had too much data to backup for their 120MB capacity and looked into the media cost of Travan, it was plain that it was too high and that the number of cartridge changes would still be inconvenient.
That's when I bought a refurbished SCSI DDS-2 autoloader (I was already using a SCSI hard disk) and switched to BackAgain/2. I am now using a DDS-4 autoloader (up to 8 tapes each holding 20GB without compression), bought for a song on eBay, with BackAgain/2000, which handles EAs, open files, and networking security information just fine (now abandonware, but demo versions all over the place and registration keys available without looking too hard). The last lot of brand-new IBM 20GB tapes cost $3.50 each. PCI-bus SCSI cards are cheap.
Now time has changed. The standard user doesn't seem to have SCSI tape drives in most cases and people are shifting to use CD/DVD or just USB/MSD or simple "hard disk" drives for backup. This makes it easy to come up with even a rexx-based solution. Indeed, it is something I am interested in a) using and b) perhaps developing.
Hard disks are too fragile for reliable backup -- no more reliable than the "working" media. Typically they are connected to the same controller as the "working" media, so the backup could be as corrupted as the original. (My tape drive and backup software are in a separate machine on the network, so I don't have the potential problem of a controller failure corrupting both backup and original.) External hard disks usually are not connected to the same controller, but they are subject to mechanical shocks that can render them and the data they hold useless; don't ask me how I know.
Even double-sided DVDs have a capacity too low for serious backup of large amounts of data.
If you really want to use hard disks (either internal or external) for backup, I suggest using RAR. And you could still burn the resulting RAR archives to DVD.