g4l (G4L) is a linux based utility that can make either a RAW (bare metal) or file-based backup.
The documentation is here.
Latest version is here.
The RAW backup will be compressed so that if taking a backup of an 8GB drive or partition, it is saved as a compressed file. All bytes will be saved including unused areas of the disk. This function is useful for capturing the disk structure (boot sector, partitions, etc.) as well as the contents of the partition(s).
The FILE backup/restore is based on partimage - a well known tool. Once you have you RAW backup, you can make a file based backup of any partition at any time. You can then restore the partition contents using partimage at a later date.