RHEL 8 New Features for Experienced Linux Administrators

Reducing Data Footprint with VDO

• Virtual data optimizer (VDO) is a Linux device mapper driver to reduces disk space usage on block devices, and minimize replication bandwidth.

• VDO includes two kernel modules, the kvdo module to control data compression, and the uds module for deduplication.

• VDO supports both inline data deduplication and compression.

• Persistent VDO mounts in /etc/fstab require using the x-systemd.requires=vdo.service mount option.

Virtual Data Optimization Phases

• VDO reduces the data footprint on storage in three phases: zero-block elimination, deduplication of redundant blocks, and data compression.

• VDO removes blocks which only include zeros, and keeps their metadata.

• The universal deduplication service (UDS) kernel module reviews the available VDO metadata to detect duplicated blocks. If a duplicated block is found, this block points to the metadata of the already available block.

• When done with zero-block elimination and deduplication, the kvdo kernel module compresses blocks using LZ4 compression and groups them on 4 KB blocks.

Structure of a VDO volume

• A VDO volume contains two parts: UDS and VDO

• The UDS part includes the name and location of each block to support the block deduplication

• The VDO part includes the VDO volume data and metadata