vdo

A set of userspace tools for managing pools of deduplicated and/or compressed block storage.

Background

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 contains a set of userspace tools for managing VDO volumes. These include "vdoformat" for creating new volumes, "vdostats" for extracting statistics from those volumes, and a variety of support and debugging tools which should not be necessary during ordinary operation.

History

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 dm-vdo.

Documentation

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

Releases

The master branch of this repository is intended to be compatible with the most recent version of the Linux kernel. These packages are available in active Fedora releases with matching kernel versions.

Each older branch of this repository is intended to work with a specific release of Enterprise Linux (Red Hat Enterprise Linux, CentOS, etc.).

• 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.

Building

In order to build the user-level programs, invoke the following command from the top directory of this tree:

    make

After building the user-level programs, they may be installed in the standard locations by invoking the following command from the top directory of this tree, as the root user:

    make install

Communication Channels and Contributions

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.

Licensing

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.