The kernel module component of VDO which provides pools of deduplicated and/or compressed block storage.
VDO is a device-mapper target that provides inline block-level deduplication, compression, and thin provisioning capabilities for primary storage. VDO is managed through LVM and can be integrated into any existing storage stack.
Deduplication is a technique for reducing the consumption of storage resources by eliminating multiple copies of duplicate blocks. Compression takes the individual unique blocks and shrinks them with coding algorithms; these reduced blocks are then efficiently packed together into physical blocks. Thin provisioning manages the mapping from logical block addresses presented by VDO to where the data has actually been stored, and also eliminates any blocks of all zeroes.
With deduplication, instead of writing the same data more than once each duplicate block is detected and recorded as a reference to the original block. VDO maintains a mapping from logical block addresses (presented to the storage layer above VDO) to physical block addresses on the storage layer under VDO. After deduplication, multiple logical block addresses may be mapped to the same physical block address; these are called shared blocks and are reference-counted by the software.
With VDO's compression, blocks are compressed with the fast LZ4 algorithm, and collected together where possible so that multiple compressed blocks fit within a single 4 KB block on the underlying storage. Each logical block address is mapped to a physical block address and an index within it for the desired compressed data. All compressed blocks are individually reference-counted for correctness.
Block sharing and block compression are invisible to applications using the storage, which read and write blocks as they would if VDO were not present. When a shared block is overwritten, a new physical block is allocated for storing the new block data to ensure that other logical block addresses that are mapped to the shared physical block are not modified.
This repository includes the kvdo module, which can be built and loaded as an out-of-tree kernel module. This module implements fine-grained storage virtualization, thin provisioning, block sharing, compression, and memory-efficient duplicate identification.
VDO was originally developed by Permabit Technology Corp. as a proprietary set of kernel modules and userspace tools. This software and technology has been acquired by Red Hat and relicensed under the GPL (v2 or later). The kernel module has been merged into the upstream Linux kernel as the dm-vdo devive mapper target. The source for this module can be found in drivers/md/dm-vdo/.
- RHEL9 VDO Documentation
- RHEL8 VDO Documentation
- RHEL7 VDO Integration Guide
- RHEL7 VDO Evaluation Guide
This repository is no longer being updated for newer kernels.
The most recent version of this project can be found in the upstream Linux kernel, as the dm-vdo module. Each existing branch of this repository is intended to work with a specific release of Enterprise Linux (Red Hat Enterprise Linux, CentOS, etc.).
| Version | Intended Enterprise Linux Release |
|---|---|
| 6.1.x.x | EL7 (3.10.0-*.el7) |
| 6.2.x.x | EL8 (4.18.0-*.el8) |
| 8.2.x.x | EL9 (5.14.0-*.el9) |
- Pre-built versions with the required modifications for older Fedora releases
can be found here
and can be used by running
dnf copr enable rhawalsh/dm-vdo.
The latest version of this project is available in the Linux kernel as the dm-vdo module starting in version 6.9. If you have a VDO volume created with the kvdo module, be sure to shut it down cleanly before switching to the dm-vdo module. Failure to do so may result in issues including loss of data.
As with any upgrade, it is advisable to create a snapshot of the device before upgrading to the new module.
In order to build the kernel modules, invoke the following command from the top directory of this tree:
make -C /usr/src/kernels/`uname -r` M=`pwd`
To install the compiled module:
make -C /usr/src/kernels/`uname -r` M=`pwd` modules_install
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There is a dkms.conf template that can be used in the kvdo.spec file which can take care of rebuilding and installing the kernel module any time a new kernel is booted.
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Patched sources that work with certain older upstream kernels can be found here.
Community feedback, participation and patches are welcome to the vdo-devel repository, which is the parent of this one. This repository does not accept pull requests.
GPL v2.0 or later. All contributions retain ownership by their original author, but must also be licensed under the GPL 2.0 or later to be merged.