This approach has a number of disadvantages, which DRBD may help offset: Shared cluster storage comparison Ĭonventional computer cluster systems typically use some sort of shared storage for data being used by cluster resources.
A multiple primary (multiple read/write nodes) configuration requires the use of a distributed lock manager. ĭRBD allows for load-balancing configurations, allowing both nodes to access a particular DRBD in read/write mode with shared storage semantics. It integrates with virtualization solutions such as Xen, and may be used both below and on top of the Linux LVM stack. 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.ĭRBD is often deployed together with the Pacemaker or Heartbeat cluster resource managers, although it does integrate with other cluster management frameworks. When the failed ex-primary node returns, the system may (or may not) raise it to primary level again, after device data resynchronization.
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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. Should the primary node fail, a cluster management process promotes the secondary node to a primary state. All read I/O is performed locally unless read-balancing is configured. The secondary node(s) then transfers data to its corresponding lower-level block device.
Writes to the primary node are transferred to the lower-level block device and simultaneously propagated to the secondary node(s). DRBD layers logical block devices (conventionally named /dev/drbd X, where X is the device minor number) over existing local block devices on participating cluster nodes.
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