Information Technology Reference
In-Depth Information
Before going too much further, it's important to cover several basics of storage:
Local storage versus shared storage
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Common storage array architectures
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RAID technologies
Midrange and enterprise storage array design
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Protocol choices
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We'll start with a brief discussion of local storage versus shared storage.
Comparing Local Storage with Shared Storage
An ESXi host can have one or more storage options actively coni gured, including the following:
Local SAS/SATA/SCSI storage
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Fibre Channel
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Fibre Channel over Ethernet (FCoE)
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iSCSI using software and hardware initiators
NAS (specii cally, NFS)
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Ini niBand
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Traditionally, local storage has been used in a limited fashion with vSphere because so many
of vSphere's advanced features—such as vMotion, vSphere HA, vSphere DRS, and vSphere
FT—required shared external storage. With vSphere Auto Deploy and the ability to deploy ESXi
images directly to RAM at boot time coupled with host proi les to automate the coni guration,
in
some
environments local storage from vSphere 5.0 serves even less of a function than it did in
previous versions.
With vSphere 5.0, VMware introduced a way to utilize local storage though the installation
of a virtual appliance called the vSphere Storage Appliance, or simply VSA. At a high level, the
VSA takes local storage and presents it back to ESXi hosts as a shared NFS mount. There are
some limitations however. It can be coni gured with only two or three hosts, there are strict
rules around the hardware that can run the VSA, and on top of this, it is licensed as a separate
product. While it does utilize the underused local storage of servers, the use case for the VSA
simply is not valid for many organizations.
vSphere 5.5, however, has two new features that are signii cantly more relevant to organiza-
tions than the VSA. vSphere Flash Read Cache and VSAN both take advantage of local storage,
in particular, local
l ash
storage. vSphere Flash Read Cache takes l ash-based storage and allows
administrators to allocate portions of it as a read cache for VM read I/O. VSAN extends on the
idea behind the VSA and presents the local storage as a distributed datastore across many hosts.
While this concept is similar to the VSA, the use of a virtual appliance is not required, nor are
NFS mounts; it's entirely built into the ESXi hypervisor. Think of this as shared
internal
storage.
Later in this chapter we'll explain how VSAN works and you can i nd information on vSphere
Flash Read Cache in Chapter 11, “Managing Resource Allocation.”
So, how carefully do you need to design your local storage? The answer is simple—generally
speaking, careful planning is not necessary for storage local to the ESXi installation. ESXi stores
very little locally, and by using host proi les and distributed virtual switches, it can be easy and
