VMware Distributed Resource Scheduler (DRS)
Now that I've piqued your interest with the introduction of VMotion, let me introduce VMware Distributed Resource Scheduler (DRS). If you think that VMotion sounds exciting, your anticipation will only grow after learning about DRS. DRS, simply put, is a feature that aims to provide automatic distribution of resource utilization across multiple ESX hosts that are configured in a cluster. An ESX Server cluster is a new feature in VMware Infrastructure 3. The use of the term cluster often draws IT professionals into thoughts of Microsoft Windows Server clusters. However, ESX Server clusters are not the same. The underlying concept of aggregating physical hardware to serve a common goal is the same, but the technology, configuration, and feature sets are very different between ESX Server clusters and Windows Server clusters.
An ESX Server cluster is an implicit aggregation of the CPU power and memory of all hosts involved in the cluster. Once two or more hosts have been assigned to a cluster, they work in unison to provide CPU and memory to the virtual machines assigned to the cluster. The goal of DRS is to provide virtual machines with the required hardware resources while minimizing the amount of contention for those resources in an effort to maintain good performance levels.
DRS has the ability to move running virtual machines from one ESX Server host to another when resources from another host can enhance a virtual machine's performance. Does that sound familiar? It should, because the behind-the-scenes technology for DRS is VMware VMotion. DRS can be configured to automate the placement of each virtual machine as it is powered on as well as to manage the virtual machine's location once it is running. For example, let's say three servers have been configured in an ESX Server cluster with DRS enabled. When one of those servers begins to experience a high contention for CPU utilization, DRS will use an internal algorithm to determine which virtual machine(s) will experience the greatest performance boost by being moved to another server with less CPU contention. Figure 1.6 outlines the automated feature of DRS.
Figure 1.6 VMware Distributed Resource Scheduler (DRS) aims to maintain balance and fairness of resource utilization for virtual machines running within an ESX Server cluster.
Chapter 9 dives deeper into the configuration and management of DRS on an ESX Server cluster.
VMware High Availability (HA)
With the introduction of the ESX Server cluster, VMware has also introduced a new feature called VMware High Availability (HA). Once again, by nature of the naming conventions (clusters, high availability), many traditional Windows administrators will have preconceived notions about this feature. Those notions, however, are premature in that VMware HA does not function like a high-availability configuration in Windows. The VMware HA feature provides an automated process for restarting virtual machines that were running on an ESX Server at a time of complete server failure. Figure 1.7 depicts the virtual machine migration that occurs when an ESX Server that is part of an HA-enabled cluster experiences failure.
Figure 1.7 The VMware High Availability (HA) feature will power on any virtual machines that were previously running on an ESX Server that has experienced server failure.
The VMware HA feature, unlike DRS, does not use the VMotion technology as a means of migrating servers to another host. In a VMware HA failover situation, there is no anticipation of failure; it is not a planned outage and therefore there is no time to perform a VMotion. VMware HA does not provide failover in the event of a single virtual machine failure. It provides an automated restart of virtual machines during an ESX Server failure.
Chapter 10 will explore the configuration and working details of VMware High Availability.
VMware Consolidated Backup (VCB)
One of the most critical aspects to any network, not just a virtualized infrastructure, is a solid backup strategy as defined by a company's disaster recovery and business continuity plan. VMware Consolidated Backup (VCB) is a Windows application that provides a LAN-free Fibre Channel or iSCSI-based backup solution that offloads the backup processing to a dedicated physical server. VCB takes advantage of the snapshot functionality in ESX Server to mount the snapshots into the file system of the dedicated VCB server. Once the respective virtual machine files are mounted, entire virtual machines or individual files can be backed up using third-party backup tools. VCB scripts integrate with several major third-party backup solutions to provide a means of automating the backup process. Figure 1.8 details a VCB implementation.
Figure 1.8 VMware Consolidated Backup (VCB) is a LAN-free online backup solution that uses a Fibre Channel or iSCSI connection to expedite and simplify the backup process.
In Chapter 10 you'll learn how to use VCB to provide a solid backup and restore practice for your virtual infrastructure.
Real World Scenario
Virtual Infrastructure 3 vs. VMware Server (and the Others)The Virtual Infrastructure 3 (VI3) product holds a significant advantage over most other virtualization products because virtualization on VI3 does not require a host operating system. Products like VMware Server and Microsoft Virtual Server 2005 both require an underlying operating system to host the hypervisor.
The lack of the host operating system in VI3 offers additional stability and security. Without an underlying operating system like Windows, there is less concern for viruses, spyware, and unnecessary exposure to vulnerabilities.
With products like VMware Server (which require a host operating system), limitations from the host operating systems spill into the virtualization deployment. For example, installing VMware Server on Windows Server 2003 Web edition would establish two processors and 2GB of RAM limitations on VMware Server, despite its ability to use up to 16 processors and 64GB of RAM. At the same time, however, there's the advantage that hosted products have over the bare metal install of ESX Server. The existence of the host operating system greatly extends the level of hardware support on which the hypervisor will run. If the host operating system offers support, then the virtual machine will too. A great example of this hardware support is to look at the use of USB. ESX Server does not support USB, while VMware Server (and Workstation) includes support. Since the underlying host understands the USB technology, the virtual machines will also offer support.
In all, each of the virtualization products has its place in a network infrastructure. The Virtual Infrastructure 3 product is more suited to the mission-critical enterprise data center virtualization scenario, while the VMware Server product is best for noncritical test or branch office scenarios. And of course you cannot forget the best part of VMware Server: it's free!
The Bottom Line
Identify the role of each product in the VI3 suite. Now that you've been introduced to the products included in the VMware Infrastructure 3 suite, we can begin discussing the technical details, best practices, and how-tos that will make your life as a virtual infrastructure administrator a whole lot easier. This chapter has shown that each of the products in the VI3 suite plays an integral part in the overall process of creating, managing, and maintaining a virtual enterprise. Figure 1.9 highlights the VI3 product suite and how it integrates and interoperates to provide a robust set of tools upon which a scalable, reliable, and redundant virtual enterprise can be built.