Incremental (delta) backup of a encrypted data

Solution 1:

First, not the whole container is changed when you edit a small file. This often comes up in connection with Dropbox. Dropbox only uploades changed blocks (TrueCrypt encryption is block cipher) from the Container. Here is a thread in the dropbox forum talking about that. But I don't know if there are incremental backup solutions sophisticated enough to look for changed blocks in files.

Second, you could take a backup of the mounted container on another encrypted drive. Standard backup software should suffice.

Solution 2:

You said you're using Crashplan. It does byte-level analysis of the changes within files and stores only the changes within each file, so you're already getting the benefit of an incremental backup.

If you're worried that adding a 14 byte file within a TrueCrypt container changes 22K bytes in the container, that's because very small files will produce disproportionately large changes to the filesystem. For example, the filesystem might be using 16K clusters, so the smallest file will affect a 16K block. In addition, the metadata and journaling adds more overhead. Try adding a 200K file, and the overhead will be proportionately much smaller.

Solution 3:

As changes in the Truecrypt volume only occur to regions where file changes has been written to, an efficient backup tool that detects binary differences for incremental backups should do the job.

What tool in detail depends on your operating system.