The Datto Block Driver (dattobd) solves the above problems and brings functionality similar to VSS on Windows to a broad range of Linux kernels. Dattobd is an open source Linux kernel module for point-in-time live snapshotting. Dattobd can be loaded onto a running Linux machine (without a reboot) and creates a COW file on the original volume representing any block device at the instant the snapshot is taken. After the first snapshot, the driver tracks incremental changes to the block device and therefore can be used to efficiently update existing backups by copying only the blocks that have changed.
Sounds interesting.