Mohamed Hamad is a Global Knowledge instructor who teaches and blogs from Global Knowledge Egypt.
A blade server system is a self-contained system including a number of computer units designed for high-performance and high-capacity computing. Blade servers allow more processing power in less space, which simplifies cabling, storage, and maintenance. Blades are often used for grid computing.
The advantage of blade servers is not only that one “cabinet” houses multiple servers that share a power source and other components but also from the consolidation of related resources, such as storage and networking equipment, into a smaller architecture than would be the case with a farm of regular servers.
Blade servers are good choice when deciding which server type to implement virtual infrastructure with VMware, but care should be considered when implementing HA “High Availability” cluster on blade servers.
As VMware HA Cluster can support up to thirty-two ESX/ESXi servers in a one cluster, the first five added servers to the cluster take the role of Primary Node. The Primary Nodes hold cluster settings and all “node states”. The data a Primary Node holds is stored in a persistent database and synchronized between primaries. An example of node state data would be host resource usage. In case vCenter is not available, the Primary Nodes will always have a very recent calculation of the resource utilization and can take this into account when a failover needs to occur.
If one of the primaries fails then one of the secondary nodes is randomly selected to be a Primary Node by contacting one of the remaining primaries. Since the loss of all Primaries at the same time may leave the HA cluster unfunctional, when designing HA cluster in a multiple chassis divide hosts over all blade chassis and never exceed four hosts per chassis to avoid having all primary nodes in a single chassis.