Backup with mixed incremental and differential strategies?
Solution 1:
Have you taken a look at rdiff-backup?
http://rdiff-backup.nongnu.org
rdiff-backup backs up one directory to another, possibly over a network. The target directory ends up a copy of the source directory, but extra reverse diffs (ie. differential backup) are stored in a special subdirectory of that target directory, so you can still recover files lost some time ago.
The idea is to combine the best features of a mirror and an incremental backup.
rdiff-backup also preserves subdirectories, hard links, dev files, permissions, uid/gid ownership, modification times, extended attributes, acls, and resource forks.
Also, rdiff-backup can operate in a bandwidth efficient manner over a pipe, like rsync. Thus you can use rdiff-backup and ssh to securely back a hard drive up to a remote location, and only the differences will be transmitted. Finally, rdiff-backup is easy to use and settings have sensical defaults.
Solution 2:
Dirvish does what you want in terms of incremental backups, and indexing backups with a utility to search them