Information Technology Reference
In-Depth Information
The beauty of a virtual disk is that it can be manipulated in many ways that a physical
disk cannot. For example, it can be easily copied and backed up because it is made as a single
file. It can even be made into a dynamically sized drive, where the capacity can increase or
decrease depending on the usage requirements. That last part is obviously impossible for a
physical drive because it is already constrained to its maximum storage capacity. But there are
of course downsides to the virtual disk. Among other limitations, the virtual disk capacity is
limited by that of the host's capacity, as will be discussed in the next section.
Limits
Despite the flexibility of virtual disks, they are not without limitation. For example, dynamic
capacity is a great feature that optimizes the virtual disk capacity by keeping it to its actual
size requirement rather than allocating a fixed amount of space that may never be used or
may not be enough, leading to the creation of another virtual disk in order to cope with the
capacity requirements. The obvious limitation of dynamic capacity is the actual capacity of
the host's physical hard drive, which contains other files as well. This is less of a problem in
enterprise solutions that employ large data centers dedicated to storage capacity where they
can simply stripe the virtual disk file across multiple physical drives.
A big problem that can be encountered when employing virtual disks, especially in older
systems, is the file system limitation. Since the virtual disk must be a single contiguous file,
it is not advisable to be used in systems that employ FAT/FAT32 or similar file systems that
cannot support files larger than 4 gigabytes. It is still possible, providing the file size limit is
not violated, so using dynamically sized virtual disks would not be appropriate. However,
multiple instances of smaller-capacity virtual disks can be used. It is advisable to use NTFS
and similar file systems so that all the benefits of the virtual disk can be enjoyed.
There are two kinds of virtual drives, the fixed disk and the dynamic disk. The fixed
disk is obviously fixed in size, and the capacity is specified during creation, and the
dynamic disk expands with use. The fixed disk is in every way similar to the physical
drive, even in performance. However, the dynamic disk is slower than the fixed disk and
has a substantially higher chance for data fragmentation. A dynamic disk contains a lock
allocation table that expands along with the contents of the disk, so a fully expanded
dynamic virtual disk will be a bit larger compared to a fixed virtual disk with the same
usable capacit y.
Virtual Switches
Virtual networking components are not easy to comprehend without an actual back-
ground in and understanding of networking in general first. So let's do a little review.
First of all, networking is just a connection between shared resources, systems, and ser-
vices, which are usually connected through wired or wireless medium. This is the same
theory applied to the virtual or logical environment. But there is a catch. You must be
able to tell the difference between a virtual and physical adapter and how they can be
linked together through the virtual switching fabric being implemented by your virtual-
ization provider. There are minor differences on how each provider implements switching
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