DM-Clone Target Added To Linux 5.4 For Efficient Remote Replication Of A Block Device

Added to the device mapper (DM) code with the Linux 5.4 kernel is an interesting addition that benefits those wanting to carry out some interesting use-cases around remote replication of block devices.

As explained in the original patch proposal for dm-clone, "dm-clone produces a one-to-one copy of an existing, read-only device (origin) into a writable device (clone): It presents a virtual block device which makes all data appear immediately, and redirects reads and writes accordingly. The main use case of dm-clone is to clone a potentially remote, high-latency, read-only, archival-type block device into a writable, fast, primary-type device for fast, low-latency I/O. The cloned device is visible/mountable immediately and the copy of the origin device to the clone device happens in the background, in parallel with user I/O."

More details on dm-clone can be found via the newly-added documentation.

The dm-clone target with Linux 5.4 is the primary new device mapper feature while the pull also has DM crypt changes, various fixes, and minor optimizations.