[dm-devel] [RFC PATCH 0/1] dm: add clone target
Nikos Tsironis
ntsironis at arrikto.com
Tue Jul 9 14:15:21 UTC 2019
This patch adds the dm-clone target, which allows cloning of arbitrary
block devices.
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.
For example, one could restore an application backup from a read-only
copy, accessible through a network storage protocol (NBD, Fibre Channel,
iSCSI, AoE, etc.), into a local SSD or NVMe device, and start using the
device immediately, without waiting for the restore to complete.
When the cloning completes, the dm-clone table can be removed altogether
and be replaced, e.g., by a linear table, mapping directly to the clone
device.
dm-clone is optimized for small, random writes, with size equal to
dm-clone's block/region size, e.g., 4K.
For more information regarding dm-clone's operation, please read the
attached documentation.
A preliminary test suite for dm-clone can be found at
https://github.com/arrikto/device-mapper-test-suite/tree/feature-dm-clone
Nikos Tsironis (1):
dm: add clone target
Documentation/device-mapper/dm-clone.rst | 334 +++++
drivers/md/Kconfig | 13 +
drivers/md/Makefile | 2 +
drivers/md/dm-clone-metadata.c | 991 +++++++++++++
drivers/md/dm-clone-metadata.h | 158 +++
drivers/md/dm-clone-target.c | 2244 ++++++++++++++++++++++++++++++
6 files changed, 3742 insertions(+)
create mode 100644 Documentation/device-mapper/dm-clone.rst
create mode 100644 drivers/md/dm-clone-metadata.c
create mode 100644 drivers/md/dm-clone-metadata.h
create mode 100644 drivers/md/dm-clone-target.c
--
2.11.0
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