Some time ago, a friend's house was broken into, and some bits and pieces were stolen. One of those pieces was the family's laptop with six or seven years of digital photographs stored on it. Next to the laptop lay a stack of DVDs on which my friend's wife wanted to backup the photos and some other personal data.
Unfortunately, it was to be the very first backup of the laptop. With the thief went all the photographs of the kids' lives. It is very unfortunate (and exceedingly stupid, being an IT guy!) that he didn't do anything in terms of backup.
As many of you know, I'm almost paranoid in terms of backing up my data, and I care a great deal for where I locate the data I backup; it is useless to keep the backup next to the computer(s) you are backing up: theft and fire can take care of both very quickly. Keeping current backups off-site is easy, if you remember to swap the data carriers once in a while, but it is a bit of a pain.
Amazon (yes, the book people) have a service called S3. You apply for an S3 account with your regular Amazon credentials (e-mail address and password), and they offer as much storage as you want, for as long as you need it.
What makes S3 unique, is that you don't pay a flat fee: you pay for what you use. Every GB of data you store costs USD 0.15 (or 0.18 for Europeans) per month. Every GB you upload or download costs USD 0.10. Knowing that, you can easily calculate what backing up your data will cost you per year (use the Amazon calculator as a guide).
With Amazon S3, and end- user can't do very much: you need tools to deposit and access data, and that is where JungleDisk comes in. JungleDisk is a marvellous little program, which costs a one-time fee of USD 20.00. It is easy to set up, and JungleDisk assists you with the process of signing up for Amazon S3 by pointing you to the correct URLs at the Amazon web sites. If you use a single S3 key with it, you can use JungleDisk from your Linux, Mac OS X and your Linux computer at the same time if you like.
You give JungleDisk your S3 key and it handles the data management on your S3 account for you. So for example, you can use JungleDisk to backup your files at home, and retrieve them on your laptop at the office. JungleDisk maps your S3 storage onto a drive (on Windows) or a volume (on Mac).
On Linux you use the command-line program (jungledisk) to mount your S3 storage using FUSE. With this, you can, for example, rsync your backups into JungleDisk, which then transparently uploads those to Amazon's S3 storage. Additionally, JungleDisk provides a WebDAV compatible service that you access via TCP port 2667 from the loopback interface: You access the WebDAV interface from Windows, Mac OSX finder, or from Linux. Even with cadaver if you want to:
$ cadaver http://localhost:2667/ ...
The JungleDisk GUI (available on all platforms) offers automatic backups. The buckets stored on the S3 servers are encrypted by Amazon's service. Theoretically it is possible for Amazon employees to access that data, but it isn't very likely they'd do that. JungleDisk supports an additional AES encryption on the files you submit to it.
The way this works is like this: you configure JungleDisk with an encryption key, effectively a passphrase you set (don't use a comma in it) with which JungleDisk encrypts the files transparently between itself and S3. When you attempt to access a file (via JungleDisk), it transparently decrypts it with your key, giving you the original data. You don't have to manually encrypt the files (with GPG or whatever): JungleDisk handles the encryption for you. Amazon S3 allows you to divide your online storage space into multiple buckets. Each bucket has its own set of files and directories that are completely separate from all other buckets. You can only access a single bucket at a time within Jungle Disk, and you cannot copy files and folders between buckets. Most users should be able to use just a single bucket for all their files, even when using Jungle Disk on multiple machines. However, Jungle Disk does allow you to create alternate buckets under your account if desired. JungleDisk has good documentation, some answers, is actively supported and has an active support forum. You can get started immediately, by downloading JungleDisk and trying it for a month; but you will of course require an Amazon S3 account. There are alternative services to S3, some of them even free of charge, but remember: you get what you pay for.