Practical Cloud Knowledge: Install, Configure, and Manage - Deploying and Managing a Cloud Infrastructure - page 216

Snapshots and Cloning Creating snapshots and cloning are good ways of creating backups
of a virtual machine. Snapshots take a sort of photograph of the current state of the machine
that you can restore at a later date. This is very convenient for reverting to a previous work-
ing state, especially if some settings that caused some undesired effects in the machine have
been changed. Cloning, on the other hand, creates a full copy of the virtual machine as well
as all of its files and settings. Unlike the snapshot, which is still connected to the original vir-
tual machine, the clone is fully independent and can be deployed any time, even in a totally
different virtual environment or host from that of the original.
Image Backups vs. File Backups The two types of backups are image and file backups.
File backups are selective in nature, meaning that backups are made of select files that are
deemed important while other files are not backed up. The backups are in the form of cop-
ies of the file itself and not some interpretation of it, so it is a one-to-one copy. The back-
ups are often stored in media or in places separate from the original location, such as an
external disk or tape backup or even flash memory and optical media. Since only selected
files are backed up, the resulting backup repository is relatively small compared to that of
a total backup.
Image backup is a total and all-encompassing kind of backup. The method involves creat-
ing a disk image from the disk that needs to be backed up. Everything is captured by the
backup, including unnecessary files such as temporary files, cache content, recycle bin
contents, and even all of the viruses and malware if any. It is a total backup but with many
drawbacks. One is that it takes up so much space, and then it takes time to create, so it can
be done only periodically, like once a day. This means that you could lose all of your work
if you are only halfway through the day and something bad happens. You would then have
to revert to yesterday's backup, whereas for file backups, only the modified files need to be
backed up again.
Virtual Disks Virtual disks are the logical counterparts of physical hard disks. They are
used in the same way as the physical ones, and for the guest operating system they would
appear as physical disks. The virtual disks are created by the hypervisor as a single file
located on the host's hard drive and as such can be ported or even copied.
Virtual Switches Virtual switches are the logical counterparts of physical switches with
some differences that are due mainly to enable enhanced security. For example, virtual
switches are logically isolated from each other, they cannot be cascaded, and there is no
mechanism for a virtual switch to map a port that connects to another virtual switch; it can
only map ports unto itself. This keeps each switch isolated from other switches and prevents
bad connections that attackers can exploit. There is also no need to cascade switches because
a virtual switch can have as many ports as required, as opposed to the limited number of
ports physical switches have. Only one virtual switch can be attached to a physical NIC.
VLAN A virtual local area network, contrary to what the name might imply in the con-
text of virtualization and cloud computing, is not the local area network formed when you
connect virtual machines in the same host together. That is still referred to as a virtual net-
work. A VLAN is actually a further subdivision of a larger network that is meant to work