The Distributed Replicated Block Device (DRBD) is a technology which makes block devices into component building blocks for high availability (HA) clusters. DRBD can mirror a whole block device over an assigned network to a second block device, and can therefore be considered a type of network-based RAID-1. In effect, DRBD provides a form of virtual shared storage between two computers. DRBD is open source software developed by Linbit and made available under the GNU GPL v2 license.

This list of features provided by DRBD has been adapted form the DRBD website:

• May be used to add redundancy to existing deployments
• Fully synchronous, memory synchronous or asynchronous modes of operation
• Masking of local IO errors
• Shared secret to authenticate the peer upon connect
• Bandwidth of background resynchronization tunable
• Automatic recovery after node, network, or disk failures
• Efficient resynchronization, only blocks that were modified during the outage of a node
• Short resynchronization time after the crash of an active node, independent of the device size
• Automatic detection of the most up-to-date data after complete failure
• Integration scripts for use with Heartbeat
• Dual primary support for use with GFS/OCFS2
• Configurable handler scripts for various DRBD events
• Online data verification
• Optional data digests to verify the data transfer over the network
• Integration scripts for use with Xen
• Usable on LVM's logical volumes. Usable as physical volume for LVM
• Integration scripts for LVM to automatically take a snapshot before a node becomes the target of a resynchronization
• Dependencies to serialize resynchronization, in case of default all devices in parallel
• Heartbeat integration to outdate peers with broken replication links, avoids switchovers to stale data
• Many tuning parameters allow to optimize DRBD for specific machines, networking hardware, and storage subsystem
• Integration scripts for use with RedHat Cluster (excl. the GUI tools)
• Existing file systems can be integrated into new DRBD setups without the need of copying
• Support for a third, off-site node for disaster recovery (since 8.3)
• Transfer between DRBD nodes can be secured using standard OS means like IPSec or OpenVPN
• Standard OS block device encryption can be used on top of DRBD devices
• A DRBD device might be used as a PV for LVM