Table of Contents
The Distributed Replicated Block Device (DRBD) is a software-based, shared-nothing, replicated storage solution mirroring the content of block devices (hard disks, partitions, logical volumes etc.) between servers.
DRBD mirrors data
In real time. Replication occurs continuously, while applications modify the data on the device.
Transparently. The applications that store their data on the mirrored device are oblivious of the fact that the data is in fact stored on several computers.
Synchronously or asynchronously. With synchronous mirroring, a writing application is notified of write completion only after the write has been carried out on both computer systems. Asynchronous mirroring means the writing application is notified of write completion when the write has completed locally, but before the write has propagated to the peer system.
DRBD's core functionality is implemented by way of a Linux kernel module. Specifically, DRBD constitutes a driver for a virtual block device, so DRBD is situated “right near the bottom” of a system's I/O stack. Because of this, DRBD is extremely flexible and versatile, which makes it a replication solution suitable for adding high availability to just about any application.
![[Important]](images/important.png) | Important |
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DRBD is, by definition and as mandated by the Linux kernel architecture, agnostic of the layers above it. Thus, it is impossible for DRBD to miraculously add features to upper layers that these do not possess. For example, DRBD cannot auto-detect file system corruption or add active-active clustering capability to file systems like ext3 or XFS. |
