Does LUKS decrypt the whole hard disk at the time of boot?
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When I boot the system after providing my decryption password, does LUKS decrypt the whole hard drive ? Or just use a file system driver to lazily decrypt the data on demand and as it is accessed ?
Decryption of the whole hard drive would require reading the whole hard drive.
The dm-crypt wikipedia page states that dm-crypt is a device mapper target, hence a block device.
Since the real file system (ext4, btrfs, ...) lay on top of that and is not even aware of the underlying block device, it has no reason to read (and decrypt) unneeded blocks.
Decryption of the whole hard drive would require reading the whole hard drive.
The dm-crypt wikipedia page states that
dm-cryptis a device mapper target, hence a block device. Since the real file system (ext4,btrfs, ...) lay on top of that and is not even aware of the underlying block device, it has no reason to read (and decrypt) unneeded blocks.