-: In the last lesson, we covered backups
and the most commonly used backup media,
known as the backup tape.
Now, while you don't need to know the specific of tapes
like their sizes and capacities because those vary greatly,
you do need to have a good idea
of the method of rotating tapes,
which means how are we going to determine
how long a tape is going to be kept
and when it can be overwritten?
Now, there are three main rotation schemes
that we're going to cover in Security Plus.
We have the 10 tape rotation,
the grandfather-father-son, and the towers of Hanoi.
Now, the 10 tape rotation is a simple method
that provides easy access to the data that's been backed up.
It could be accomplished during a two-week backup period.
Why is it called a 10 tape rotation
instead of a 14 tape rotation?
Well, because most companies are open Monday through Friday,
so weekends don't count.
If you wanted to do it seven days a week for two weeks,
you could simply call it a 14 tape rotation instead
and use 14 tapes.
Either way, the concept is the same.
Each tape is going to be used once per day for two weeks,
and then, the entire set is reused again.
This means after two weeks,
you don't have anymore backups though.
Now, the second method is known as a grandfather-father-son,
and it's a backup rotation system that's very commonly used.
It's actually one of my favorites.
When attempting to use this design,
there are three sets of backup tapes
that have to be defined.
Usually, we call these the daily, the son;
the weekly, the father; and the monthly, the grandfather.
These tapes are then rotated on a daily basis,
and the last one of the week
will be graduated to father status.
Then, these tapes, the weekly ones,
are then rotated on a weekly basis,
and after four weeks, they become the monthly,
or the grandfather, and that is how we get
our grandfather, fathers, and sons.
Generally, your monthly tapes are kept offsite,
and this will allow you to ensure that they're safe
in case of an emergency at your regular facility or site.
I mean, it would be horrible if your site burned down
and you couldn't do any backups because all your tapes
were in the server room, right?
So you want to make sure you have some good
offsite backups as well.
Now, the third type we have is called the towers of Hanoi,
and this a rotation system that's based on the puzzle
called the towers of Hanoi
that you might've played as a kid.
Much like the grandfather, father, and son,
this system also uses three sets of backups,
but they're rotated a bit differently.
Basically, your first tape is used every second day,
and the second tape is used every fourth day,
and the third tape is used every eighth day,
and so this system helps prevent tapes
from being worn out as quickly
as the 10 tape rotation does,
and it does allow for three different categories of backups
like the grandfather, father, and son method,
but because of this complexity,
it makes it harder to remember what tapes do I use to backup
and in which order, and then when I go to restore,
I have to figure that out as well.
For example, we might use category one in this schedule
as our differential backups and then use category two
as our incremental backups
and category three as our full backups.
You can see how this becomes difficult to keep track of,
right?
Personally, I've always favored the grandfather,
father, and son method,
and that's the one I use in most of my organizations,
but a lot of people like the towers of Hanoi,
and it's one of those things that test writers
really love to see on the exam
because of that distinctive name.
If you see a question about towers of Hanoi on the exam,
just remember, it's referring to a
backup tape rotation strategy.
Now, in addition to our tape backups,
because network storage has become so much cheaper,
and virtual machines are become much, much more common,
there's also an entire system backup
known as a snapshot.
With a snapshot, all of the applications,
the hard drives, and even the operating system
is backed up to create a full backup of the system
as a virtual disc image.
This makes it very quick
to redeploy that system onto a cloud server
or another offsite location, but it does take up
a lot of storage space,
so you need to plan for that extra storage resources
and costs that are involved in using snapshots
instead of regular backups.
Snapshots are also commonly used with virtualized systems,
so if you're running VMware or VirtualBox,
you can take a snapshot of your server
and create that full backup of the entire virtual system.
(electronic whirring)