Windows Clustering Types
Windows Server Failover cluster
In a failover cluster, if one or more of the clustered servers (nodes) fails, other nodes begin to provide service.
Quorum Witness Types
Standalone vs Clustered
SQL Cluster Types
Note: “Always On” is a marketing term for sql cluster solution.
– With Clustered VMDKs feature introduced in vSphere 7, WSFC clusters can be created on vSphere without RDMs.
– Why was RDMs needed? WSFC clusters use SCSI-3 persistent reservation commands to clustered disk resources. The command locks the volume so that only the active node is allowed to write it. But VMFS intercepts and discards these commands for traditional virtual disk.Hence the need for RDM disks acting as a mapping device for the physical LUN
– What has changed with Clustered VMDKs?
Clustered VMDK allows SCSI-3 PR commands issued to virtual disks.
vSphere Options for Shared storage
SCSI Bus sharing
Multi-Writer Disk sharing
The multi-writer option allows VMFS-backed disks to be shared by multiple virtual machines.
By default, VMFS disables multiple virtual machines from opening and writing to the same virtual disk (.vmdk file).
Note: Multi-writer feature must not be used for a clustered disk resource for WSFC.
Failover Cluster with Clustered VMDKs