Advantages and disadvantages of server virtualization Clusters

One of the most significant features of server virtualization is the ability to instantly migrate virtual machines (VMS) within a host cluster, reducing server or application system downtime. Although each major hypervisor has this function, each vendor implements a different cluster mode.

In a test environment built using Microsoft hyper-V, by building a host cluster environment, I saved countless server downtime. However, this technology also caused some problems. To this end, experts have elaborated on the three most important advantages and disadvantages of the server virtualization cluster environment.

Server virtualization cluster Advantages 1: proactive risk avoidance

I believe that the biggest advantage of a server cluster is that it can actively migrate VMS from one host to another. In this way, the running time of the server and application system can be improved.

In my environment, I will receive an alarm when the memory is insufficient, the CPU load is high, or the VM encounters high I/O pressure. If I cannot determine the real cause or the system needs to be restarted, I can take the initiative to migrate the VM to other hosts in the cluster.

If this is a single machine, or during host restart, the VM cannot be shut down; if the problem persists after the restart, I had to extend the VM downtime until I found the cause of the problem. However, in a VM cluster, the VM can be migrated to another host until the problem is solved.

Server virtualization cluster advantages 2: Reactive Fault Tolerance

Because the host in the cluster monitors All VM activities, when a node fails, the load of the failed node will be assigned to another alternative host. If it takes a long time to resolve the failure of the host, the VM will work normally as long as the healthy host that replaces it has enough resources.

In my environment, if a host fails, the VM will be automatically migrated to another node. Although the migration process is not smooth, there is almost no pause in automatic workload changes.

Server virtualization cluster advantages 3: active management

I work in a organization, so patching and upgrading must be managed very strictly. Under normal circumstances, it is difficult to coordinate the downtime of one or two physical hosts, and the complexity of shutting down more than 30 VMS on the same physical host will increase exponentially.

After switching to a single host, my wife has no need to worry about upgrading the VM from to on Sunday. At that time, I can stay at home and have a rest. Using a VM cluster, when a host is patched and restarted, the VM on it is migrated to the alternative host. After patching, the VM is migrated to the original host. In this way, we can complete cluster upgrade without stopping the entire system in a very short time in the morning.

Disadvantages of cluster host environment

Although the host cluster environment has notable advantages, it also has some shortcomings in implementation and management.

Disadvantage 1: complexity of implementation and Configuration

Complex Configuration may be the biggest disadvantage of the cluster. Creating a cluster framework, managing the connectivity between hosts, and configuring shared storage is not a simple task. It may involve multiple teams in the Organization. You may not be afraid of increasing complexity. However, it is a technical task to a large extent. However, as the complexity increases, you may miss something that affects system stability.

Disadvantage 2 of server virtualization cluster: unfavorable factors for update and upgrade

Upgrading to the latest version of the product and hardware components may also cause difficulties. Because the VM cluster connects to multiple systems, a large number of complex interactions occur between components.

Taking the update of the multi-path I/O (mpio) driver on the host as an example, this operation affects the entire cluster. First, it affects the efficiency of transferring a logical unit number (Lun) to another node. At the same time, before updating the mpio driver, the firmware of all hosts in the cluster must be upgraded. If you do not need to upgrade the FW, you must first install the HBA driver.

If it is a single machine, this can be solved through 1-2 restart. In a cluster environment, it is difficult to coordinate multiple VM servers. Upgrading the actual virtual host software must be a challenging task because of the interaction between cluster nodes and support of different software versions (such as scvmm and Protection Manager ).

In general, the manufacturer will provide detailed and step-by-step operation instructions for these complex upgrades. In most cases, the operation will be smooth.

Disadvantage 3 of server virtualization cluster: Cluster cost factors

Cost is another major consideration. To implement a virtual host cluster environment, you need to copy some of the infrastructure and maintain the ratio of the VM to the host at the same time. In addition, most vendors require a San or independent disk subsystem. Open-source iSCSI or Inexpensive Disk Arrays may be a good choice, but these options may have performance and stability problems.

In my experience, selecting a cheap route on an important infrastructure component will cause problems and cause a stumbling block. Because a special configuration is selected to work, it does not mean that the project objectives are met. If the management department is concerned about the cost, you can explain that the virtual host cluster environment can improve the normal running time and provide better services. In my opinion, if it is implemented correctly, this configuration is completely affordable.

Finally, each organization has to determine whether the VM cluster environment is suitable for its business system model. Although the VM cluster environment introduces configuration complexity, upgrade problems, and potential extra costs, your environment can benefit from enhanced server or application system availability and better management. Despite the potential difficulties or disadvantages, I believe that the effort and cost of implementing a VM cluster are worthwhile.

However, you can weigh whether you want to implement a VM cluster.