Primary development repository for the dm-vdo kernel module and related userspace tools, plus documentation, tests and packaging support for dm-vdo.

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.

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 device mapper target. The source for this module can be found in drivers/md/dm-vdo/.

Documentation can be found in the doc directory. Additional documentation can be found here:

• RHEL9 VDO Documentation
• RHEL8 VDO Documentation
• RHEL7 VDO Integration Guide
• RHEL7 VDO Evaluation Guide

This repository is the upstream source for the dm-vdo kernel module. The most recent updates enter the mainline Linux kernel through the device-mapper tree.

Userspace tools for managing dm-vdo device-mapper targets are published periodically through the vdo repository.

In order to build the entire project, invoke the following command from the src directory of this tree:

    make all archive

Source tarballs and installable RPMs will appear in the archive directory.

Patched sources that work with some older kernels can be found here.

Community feedback, participation and patches are welcome. Code contributions can be filed as pull requests and will be accepted based on review feedback and testing results. Patches can also be submitted to [email protected] using the normal kernel patch submission process.

Questions and suggestions can be filed as issues. We try to address issues and pull requests in a timely manner, but a response may sometimes take a few days. Your patience is appreciated.

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.