Server virtualization one of the most prominent feature is the ability to instantly migrate within the host cluster virtual machine (VM), to reduce server or application downtime. While each major hypervisor has this feature, but each company there are different ways to achieve the cluster.
Microsoft Hyper-V using the set up of test environment, by constructing the host cluster environment, I have saved countless server downtime. However, this technology has caused some problems. Here, TechTarget China's special expert Rob McShinsky virtual host cluster environment will be described the three most important advantages and disadvantages.
Advantages of a: active risk aversion
I believe the biggest advantage of server clusters is that it can take the initiative to migrate VM from one host to another host. In this case, you can increase server and application uptime.
In my environment, when memory, CPU load too high or very high when the virtual host I / O stress, I will receive the alert. If I'm not sure the real reason or need to restart the system, can take the initiative to VM I moved to other hosts within the cluster.
If this is a stand-alone, or in the host during the restart, VM can not shut down; If you reboot, the problem persists, I would have to extend the VM down time until I found the cause. However, in the virtual host in the cluster, VM can be migrated to other hosts until the problem is resolved.
Two advantages: the reaction of fault-tolerant
Because the cluster of all VM host monitoring activities, so when a node failure, the failure node will be assigned to another load alternative host. If you need a longer time to resolve the failure of the host's fault, replace it as long as the health of the host has sufficient resources, VM will work properly.
In my environment, if a host failure, VM will automatically migrate to another node. Although the migration process is not smooth, but almost no change in work load automatically stopped.
Three advantages: active management
I have a 7 * 24 organizations work, therefore, patches and upgrades must take a very strict management. Under normal circumstances, coordination 1-2 physical host down time has been difficult, but to shut down in the same physical host more than 30 VM's complexity will increase exponentially.
Since the switch to the single, I do not worry about my wife on Sunday morning and 1:00-6:00 in the virtual host to upgrade, at that time, I can stay home and rest. Using virtual host cluster, when the patch and reboot a host when the VM on which to migrate to alternative hosts. So after patch, VM and then migrate to the original host. This allows us in the morning on a very short period of time without turning off the system, complete cluster upgrade.
The shortcomings of the host cluster environment
Although the main advantage of the cluster environment is impressive, but it also has some shortcomings in the implementation and management.
One drawback: the complexity of implementation and configuration
Complex cluster configuration may be the biggest drawback. The establishment of the cluster framework, management, connectivity between hosts, configure shared storage is not a simple task, may involve multiple teams within the organization. You may not fear the increase in complexity, but to a large extent, all technical work; However, as complexity increases, you may miss some of the things which affect the stability of the system.
Disadvantage II: Update and Upgrade disadvantages
Upgrade to a newer version of the product and hardware components may also cause difficulties. Because the virtual host cluster to connect multiple systems, took place between various components of a large number of complex interactions.
To update the host multi-path I / O (MPIO) driver, for example, the operation will affect the entire cluster. First, it affects the logical unit number node metastasis (LUN) to another node efficiency. Meanwhile, the MPIO driver update before the cluster of all the host of the HBA card's Firmware upgrades are needed. If you do not upgrade FW, it must first install the HBA card's driver.
If you are single, this can be resolved by restarting 1-2 times. In a clustered environment, the coordination number of virtual host server is more difficult. The actual virtual host software upgrade must be a challenging task because of the cluster nodes to support interaction and the different software versions (for example, SCVMM, Protection Manager, etc.).
In general, manufacturers will offer upgrades for these complex and detailed, step by step guide to the operation of operation; the same time, in most cases, will be relatively smooth.
Three disadvantages: cost factors cluster
Cost is another major consideration. To achieve a virtual host cluster environment, you need to copy part of the infrastructure and to maintain the ratio of the virtual machine and the host. In addition, most companies need a SAN or the realization of independent disk subsystems. Or low-cost open-source iSCSI disk array may be a wise choice, but these options may have performance and stability issues.
In my experience, the key infrastructure components to choose the cheap route would create problems, causing a stumbling block. Just because a particular configuration chosen to work does not mean that to meet the project objectives. If the management worried about the cost, you can explain to them the virtual host cluster environment can increase uptime and provide better service. In my opinion, if properly implemented, this configuration is completely worthy of the cost.
Finally, each organization must determine whether the virtual host cluster environment suited to their business systems model. Although the introduction of virtual host cluster environment, the complexity of configuration, upgrade issues and potential additional costs, but can enhance your environment or application server availability and better management of the benefit. Despite the potential difficulties or disadvantage, but I believe that the implementation of the virtual host cluster efforts and costs are worth it.
We can keep the debate about the pros and cons, but you can weigh whether you want to implement virtual host cluster.