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Disaster Recovery or DR is much talked about these days however when it comes to implementing one, organizations often shy away because of the cost of such applications are prohibitive. DRBD is one gem of a technology from the open source world that has class-leading features to provide continuous replication over LAN or WAN. DRBD® refers to block devices designed as a building block to form high availability (HA) clusters. This is done by mirroring a whole block device via an assigned network. It is shown as network raid-1- DRBD. In the illustration above, the two orange boxes represent two servers that form an HA cluster. The boxes contain the usual components of a Linux™ kernel: file system, buffer cache, disk scheduler, disk drivers, TCP/IP stack and network interface card (NIC) driver. The black arrows illustrate the flow of data between these components. The orange arrows show the flow of data, as DRBD mirrors the data of a high availably service from the active node of the HA cluster to the standby node of the HA cluster. DRBD layers logical block devices (conventionally named /dev/drbdX, where X is the device minor number) over existing local block devices on participating cluster nodes. Writes to the primary node are transferred to the lower-level block device and simultaneously propagated to the secondary node. The secondary node then transfers data to its corresponding lower-level block device. All read I/O is performed locally.
Should the primary node fail, a cluster management process promotes the secondary node to a primary state. This transition may require a subsequent verification of the integrity of the file system stacked on top of DRBD, by way of a filesystem check or a journal replay. When the failed ex-primary node returns, the system may (or may not) raise it to primary level again, after device data resynchronization. DRBD's synchronization algorithm is efficient in the sense that only those blocks that were changed during the outage must be resynchronized, rather than the device in its entirety.
DRBD is often deployed together with the Heartbeat cluster manager, although it does integrate with other cluster management frameworks. It integrates with virtualization solutions such as Xen, and may be used both within and on top of the Linux LVM stack.
DRBD version 8, released in January 2007, introduced support for load-balancing configurations, allowing both nodes to access a particular DRBD in read/write mode with shared storage semantics. Such a configuration requires the use of a distributed lock manager. Why DRBD?
- DRBD has been in development for over 10 years and continues to undergo feature upgrades.
- DRBD has been officially accepted into the Linux Kernel 2.6.33.
- DRBD is simple, fast and flexible.
- DRBD is the defacto solution for data replication.
- DRBD is transaction safe technology; this means that DRBD is designed to replicate data in a reliable, secure and safe method no matter how sensitive your payload is.
- DRBD is application agnostic: It works with any application!
- DRBD has support options: Whether it be installation assistance, 24/7 support or a single support incident, LINBIT can help. Click here for more details.
- DRBD is open-source!
- DRBD is carrier grade technology (99.999% uptime
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