Databases Reference
In-Depth Information
The Breadth of Virtualization
When we talk about virtualization today, it is mostly in terms of physical servers, virtual servers,
and the virtualization software known as a hypervisor, all terms this chapter dei nes later. However,
your data center has probably had virtualization in it in some form for a long time, for the reasons
we mentioned earlier — to help increase the utilization of expensive and typically underused
physical hardware assets.
Today, most Storage Area Network hardware, SANs, use virtualization internally to abstract the
storage partitions they present a server with from their physical components, such as the different
speed hard drives it might use internally for storing data on.
While a system administrator will see an amount of usable storage on a storage partition the SAN
creates for them, the exact coni guration of the physical disks that store the data are hidden, or
abstracted, from them by a virtualization layer within the SAN.
This can be a benei t for system administrators, allowing them to quickly deploy new storage
while the SAN takes care of the underlying technical settings. For example, modern SANs will
choose to store the most regularly used data on fast disks and the less frequently used data on
slower disks. Yet, the data accessed most frequently might change over time, but by using
virtualization, the SAN can re-distribute the data based on historic usage patterns to
optimize its performance without the system administrator knowing.
Of course, this may not always be appropriate, a DBA might ask to use storage with consistent
performance metrics; but like all virtualization technologies, once the product's options and
limitations are known, an optimized coni guration can be used.
Cisco and other network vendors also use virtualization in their network hardware. You may
wonder how a collection of network cables and switches could benei t from virtualization, but
the concept of virtual LANS (VLANs) enables multiple logical networks to be transmitted over a
common set of cables, NICs and switches, removing the potential for duplicated network hardware.
Finally, believe it or not, SQL Server still uses memory virtualization concepts that date back to the
Windows 3.1 era! Windows 3.1 introduced the concept of virtual memory and the virtual address
spaces, and as discussed in Chapter 3 of this topic, it is still core to the Windows memory
management architecture that SQL Server uses today. By presenting each Windows application
with its own virtual memory address space, Windows (rather than the application) manages
the actual assignment of physical memory to applications. This is still a type of virtualization where
multiple isolated processes concurrently access a shared physical resource to increase its overall
utilization.
Platform Virtualization
Having looked at the background of virtualization and some of the reasons to use it, this section
clarii es what the term platform virtualization means, as it's the focus for the rest of this chapter.
Platform virtualization is a type of hardware virtualization whereby a single physical server can
concurrently run multiple virtual servers, each with its own independent operating system,
application environment and IP address, applications, and so on.
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