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The most common size for an HA cluster is a two-node cluster, since that is the minimum required to provide redundancy, but many clusters consist of many more, sometimes dozens of nodes. The attached diagram is a good overview of a classic HA cluster, with the caveat that it does not make any mention of quorum/witness functionality (see above).
High availability (HA) is a characteristic of a system that aims to ensure an agreed level of operational performance, usually uptime, for a higher than normal period. [ 1 ] There is now more dependence on these systems as a result of modernization.
The failure of disk hardware or a given storage node in a cluster can create a single point of failure that can result in data loss or unavailability. Fault tolerance and high availability can be provided through data replication of one sort or another, so that data remains intact and available despite the failure of any single piece of equipment.
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(s). The secondary node(s) then transfers data to ...
Availability Every request received by a non-failing node in the system must result in a response. This is the definition of availability in CAP theorem as defined by Gilbert and Lynch. [1] Note that availability as defined in CAP theorem is different from high availability in software architecture. [5] Partition tolerance
The Red Hat Cluster Suite (RHCS) includes software to create a high availability and load balancing cluster. Both can be used on the same system although this use case is unlikely. Both products, the High Availability Add-On and Load Balancer Add-On, are based on open-source community projects. Red Hat Cluster developers contribute code ...
Distributed storage, as opposed to centralized storage, typically takes the form of a cluster of storage units, with a mechanism for data synchronization and coordination between cluster nodes. Distributed storage has several advantages. [2] Scalability: support to scale the storage system horizontally by adding or removing storage units to the ...
The Linux-HA (High-Availability Linux) project provides a high-availability solution for Linux, FreeBSD, OpenBSD, Solaris and Mac OS X which promotes reliability, availability, and serviceability (RAS). [1] The project's main software product is Heartbeat, a GPL-licensed portable cluster management program for high-availability clustering. Its ...