Information Technology Reference
In-Depth Information
Availabilit y
The overall availability of your virtualized infrastructure—and by exten-
sion, the VMs running on that infrastructure—depend on the shared storage infrastructure.
Designing high availability into this infrastructure element is paramount. If the storage is not
available, vSphere HA will not be able to recover and the aggregate community of VMs can
be affected. (We discuss vSphere HA in detail in Chapter 7, “Ensuring High Availability and
Business Continuity.”)
While design choices at the server layer can make the vSphere environment relatively more
or less optimal, design choices for shared resources such as networking and storage can some-
times make the difference between virtualization success and failure. This is especially true
for storage because of its critical role. The importance of storage design and storage design
choices remains true regardless of whether you are using storage area networks (SANs), which
present shared storage as disks or logical units (LUNs); network attached storage (NAS),
which presents shared storage as remotely accessed i le systems; or a mix of both. Done cor-
rectly, you can create a shared storage design that lowers the cost and increases the efi ciency,
performance, availability, and l exibility of your vSphere environment.
This chapter breaks down these topics into the following main sections:
“Examining Shared Storage Fundamentals” covers broad topics of shared storage that are
critical with vSphere, including hardware architectures, protocol choices, and key termi-
nology. Although these topics apply to any environment that uses shared storage, under-
standing these core technologies is a prerequisite to understanding how to apply storage
technology in a vSphere implementation.
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“Implementing vSphere Storage Fundamentals” covers how storage technologies cov-
ered in the previous main section are applied and used in vSphere environments. This
main section is broken down into a section on VMFS datastores (“Working with VMFS
Datastores”), raw device mappings (“Working with Raw Device Mappings”), NFS datas-
tores (“Working with NFS Datastores”), and VM-level storage coni gurations (“Working
with VM-Level Storage Coni guration”).
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“Leveraging SAN and NAS Best Practices” covers how to pull together all the top-
ics discussed to move forward with a design that will support a broad set of vSphere
environments.
Examining Shared Storage Fundamentals
vSphere 5.5 offers numerous storage choices and coni guration options relative to previous ver-
sions of vSphere or to nonvirtualized environments. These choices and coni guration options
apply at two fundamental levels: the virtualization layer and the VM layer. The storage require-
ments for a vSphere environment and the VMs it supports are unique, making broad generaliza-
tions impossible. The requirements for any given vSphere environment span use cases ranging
from virtual servers and desktops to templates and virtual CD/DVD (ISO) images. The virtual
server use cases vary from light utility VMs with few storage performance considerations to the
largest database workloads possible, with incredibly important storage layout considerations.
Let's start by examining this at a fundamental level. Figure 6.1 shows a simple three-host
vSphere environment attached to shared storage.
It's immediately apparent that the ESXi hosts and the VMs will be contending for the shared
storage asset. In a way similar to how ESXi can consolidate many VMs onto a single ESXi host,
the shared storage consolidates the storage needs of all the VMs.
