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.
Simplicity of a shared nothing vs a shared disk cluster
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|
Here are some examples of mirror application modules:
Here are some examples of farm application modules: