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Shared nothing cluster vs shared disk cluster

Shared nothing cluster vs shared disk cluster

Shared nothing cluster vs shared disk cluster is an important point to consider when choosing a cluster solution. The deployment of a shared nothing cluster as implemented by SafeKit is much more simple than a shared disk cluster.

Comparison table
Comparison video with disaster recovery
Key differentiators of a mirror cluster with replication and failover
FAQ on Evidian SafeKit (shared nothing cluster)

Comparison table: shared nothing cluster vs shared disk cluster

Simplicity of a shared nothing vs a shared disk cluster
Architecture	Shared nothing cluster	Shared disk cluster
Product	SafeKit on Windows Linux	Clustering toolkit for shared disk
Extra hardware	No - Use internal disks of servers	Yes - Extra cost with a shared bay of disks
Application data organization	0 impact on application data organization with SafeKit. Just define directories to replicate in real-time. Even directories inside the system disk can be replicated.	Impact on application data organization. All data to recover must be localized in a special shared disk. Data in the system disk cannot be replicated.
Complexity of deployment	No - install a software on 2 servers	Yes - require specific IT skills to configure OS and shared disk
Failover	Just restart the application on the second server	Switch the shared disk. Remount the file system. Pass the recovery procedure on the file system. And then restart the application
Disaster revovery	Just put the 2 servers in 2 remotes sites connected by an extended LAN. Video of disaster recovery with a software SAN	Extra cost with a second bay of disks.New specific IT skills to configure mirroring of bays across a SAN.
Quorum and split brain	No data corruption in case of network isolation between the two servers (split brain). Cluster quorum video : no quorum server and no quorum disk	Require a special quorum disk or a third quorum server to avoid data corruption on split brain
Suited for	Software editors which want to add a simple high availabity to their application	Enterprise with IT skills and large database applications

Video comparing a shared disk cluster and a shared nothing cluster when considering disaster recovery

More information on shared nothing clusters implemented by the SafeKit software on Windows and Linux here.

Key differentiators of file replication and failover with the Evidian SafeKit mirror cluster

Evidian SafeKit mirror cluster with real-time file replication and failover
Synchronous replication		The real-time replication is synchronous with no data loss on failure This is not the case with asynchronous replication
After a server failure, fully automated failback procedure		After a server failure and a failover, the replication failback procedure is fully automatic on the failed server and without stopping the application on the only remaining server This is not the case with most replication solutions particularly with replication at the database level. Manual operations are required for resynchronizing a failed server. The application may even be stopped on the only remaining server during the resynchonization of the failed server
All clustering features		The solution includes all clustering features: server failure monitoring, network failure monitoring, software failure monitoring, automatic application restart with a quick recovery time, a virtual IP address switched in case of failure to automatically reroute clients. A clustering configuration is simply made by means of a high availability application module. There is no domain controller or active directory to configure on Windows. The solution works on Windows and Linux This is not the case with replication-only solutions like replication at the database level Quick application restart is not ensured with full virtual machines replication. In case of hypervisor failure, a full VM must be rebooted on a new hypervisor with an unknown recovery time
Replication of any type of data		The replication is working for databases but also for any files which shall be replicated This not the case for replication at the database level
File replication vs disk replication		The replication is based on file directories that can be located anywhere (even in the system disk) This is not the case with disk replication where special application configuration must be made to put the application data in a special disk
File replication vs shared disk		The servers can be put in two remote sites This is not the case with shared disk solutions
Remote sites		With remote sites, the solution works with only 2 servers and for the quorum (network isolation), a simple split brain checker is offered This is not the case for most clustering solutions where a 3^rd server is required for the quorum If both servers are connected to the same IP network through an extended LAN between two remote sites, the virtual IP address of SafeKit is working with rerouting at level 2 If both servers are connected to two different IP networks between two remote sites, the virtual IP address can be configured at the level of a load balancer. SafeKit offers a health check: the load balancer is configured with a URL managed by SafeKit which returns OK on the primary server and NOT FOUND else. This solution is implemented for SafeKit in the Cloud but it can be also implemented with a load balancer on premise Virtual IP address is not offered by replication-only solution
Uniform high availability solution		SafeKit implements a mirror cluster with replication and failover. But it imlements also a farm cluster with load balancing and failover. Thus a N-tiers architecture can me made highly available and load balanced with the same solution on Windows and Linux (same installation, configuration, administration with the SafeKit console or with the command line interface). This is unique on the market This is not the case with an architecture mixing different technologies for load balancing, replication and failover

FAQ on Evidian SafeKit (shared nothing cluster)

3 demonstrations [+]

Application high availability modules [+]

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Best use cases [+]

Distinctive advantages [+]

More on the mirror cluster [+]

More on the farm cluster [+]

SafeKit Webinar [+]

Pricing - Free trial [+]