Information Technology Reference
In-Depth Information
Figure 7.1
Each layer has its
own forms of high
availability.
App
App
App
App
Application layer
Operating system layer
OS
OS
OS
OS
Virtualization software
Virtualization layer
Physical infrastructure (switches, NICs,
servers, SANs, disks, etc.)
Physical layer
At each layer, there are tools and techniques for providing high availability and business
continuity:
At the Application layer, options include Oracle Real Application Clusters (RAC).
At the OS layer, solutions include OS clustering functionality, such as Windows Server
Failover Clustering (WSFC).
The Virtualization layer offers a number of features for high availability, including
vSphere High Availability (HA) and vSphere Fault Tolerance (FT).
At the Physical layer high availability is achieved through redundant hardware—mul-
tiple network interface cards (NICs) or host bus adapters (HBAs), multiple storage area
network (SAN) switches and fabrics, multiple paths to storage, multiple controllers in
storage arrays, redundant power supplies, and so forth.
Each of these various technologies or techniques has its own strengths and weaknesses. For
example, providing redundancy at the Physical layer is great, but it doesn't help with failures at
the Application layer. Conversely, protecting against application failures is great but won't help
much if the underlying hardware isn't redundant. As you set forth to establish high availability
for your virtualized workloads, keep in mind that there is no “one size i ts all” solution. Use the
right tool for the job based on your specii c requirements.
Given that this is a book on vSphere, we can cover only some of the various possibilities for
ensuring high availability, so we'll focus out efforts on three key technologies or techniques that
help provide high availability:
OS clustering in Microsoft Windows
ESXi host clustering using vSphere HA
VM mirroring using vSphere FT
After a discussion of these three broad areas, we discuss some areas relating to business con-
tinuity. You can i nd details relating to High Availability at the physical layer in other chapters
of this topic, such as Chapter 5, “Creating and Coni guring Virtual Networks,” and Chapter 6,
“Creating and Coni guring Storage Devices.”
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