The Bottom Line - Mastering VMware vSphere 5.5 - page 765

Solution The i rst is a cluster in a box, which is mainly used for testing or in a develop-
ment environment where both nodes of a Windows cluster run on the same ESXi host.
The second is the cluster across boxes, which is the most common form of clustering in a
virtual environment. In this coni guration, you can use Windows clustering on VMs that
are running on different physical hosts. The third is the physical-to-virtual coni guration,
where you have the best of both the physical and virtual worlds by having a Windows
clustering node on both a physical server and a virtual server.
Master It What is the key difference between NLB clusters and Windows failover
clusters?
Solution Network Load Balancing (NLB) clusters are used primarily for scaling
performance. Windows failover clusters are primarily used for high availability and
redundancy.
Use vSphere's built-in high-availability functionality. VMware Virtual Infrastructure
has high-availability options built in and available to you out of the box: vSphere High
Availability (HA) and vSphere Fault Tolerance (FT). These options help you provide better
uptime for your critical applications.
Master It What are the two types of high-availability options that VMware provides in
vSphere, and how are they different?
Solution VMware provides two forms of high availability in vSphere. vSphere HA pro-
vides a form of high availability by giving you the ability to restart any VMs that were
running on a host that crashes. vSphere Fault Tolerance (FT) uses vLockstep technology
to record and replay a running VM on another host in the cluster. Failover from the pri-
mary VM to the secondary VM is without any downtime. vSphere HA restarts the VM
in the event of failure; vSphere FT does not need to restart the VM because the secondary
VM is kept in lockstep with the primary and can take over immediately in the event of a
failure.
Recognize differences between different high-availability solutions. A high-availability
solution that operates at the application layer, like Oracle Real Application Cluster (RAC), is
different in architecture and operation from an OS-level clustering solution like Windows
failover clustering. Similarly, OS-level clustering solutions are very different from hypervisor-
based solutions such as vSphere HA or vSphere FT. Each approach has advantages and dis-
advantages, and today's administrators will likely need to use multiple approaches in their
datacenter.
Master It Name one advantage of a hypervisor-based high-availability solution over an
OS-level solution.
Solution Because a hypervisor-based solution would operate beneath the guest OS
level, it would operate independently of the guest OS and could therefore potentially sup-
port any number of different guest OSes. Depending on the implementation, hypervisor-
based solutions might be simpler than OS-level solutions. For example, vSphere HA is
generally less complex and easier to set up or coni gure than Windows failover clustering.
Understand additional components of business continuit y. There are other components of
ensuring business continuity for your organization. Data protection (backups) and replication