- [Instructor] Backups are perhaps the most important
component of any disaster recovery plan.
Most businesses today are built around data
whether it's proprietary designs,
confidential customer lists or information databases,
data drives business.
For many organizations the complete loss of their data
would be a disaster of tremendous proportions.
Backups provide organizations with a fail safe way
to recover their data in the event of a technology failure,
human error, natural disaster or other circumstances
that result in data's accidental or intentional
deletion or modification.
Backups are a crucial safety net for data driven businesses.
Organizations may backup their data in many different ways.
Traditionally organizations wrote their backups to tape
and this is still a very common practice today.
However tapes are unwieldy to manage
and modern backup approaches often use alternative storage
that has become much less expensive over the past few years.
For example, some organizations perform disk to disk backups
that write data from the primary desk to
special disks set aside for backup purposes.
Those backup disks may be in a separate facility
where it would be unlikely that the same physical disaster
would effect both the primary and backups site.
A newer trend in backups is to write backups
directly to storage provided by Cloud computing vendors
such as Amazon web services, Microsoft Azure
or their competitors.
This provides great geographic diversity,
as the backup data is stored in
separately managed facilities.
And Cloud providers usually perform their own backups
of their systems providing an added layer of protection
for customer data.
When performing a backup, there are three primary
backup types and they differ based upon the data
that they include.
Full backups as the name implies, include everything
on the media being backed up.
They make a complete copy of the data.
Differential backups supplement full backups
and create a copy of only the data that has changed
since the last full backup.
Incremental backups are similar to differential backups
but with a small twist.
Incremental backups include only those files
that have changed since the most recent full
or incremental backup.
The exam commonly includes questions about backup types,
and it's very important that you understand
not only what data is included in each backup
but also what backups would need to be restored
in the event of a disaster.
Let's take a quick look at an example.
Joe is the storage administrator for his company
and he performs a full backup of his systems
every Sunday afternoon.
He then performs differential backups every week day evening
if the system fails on Friday morning,
what backups would he need to restore?
First, Joe needs a base.
So he would need to restore the most recent full backup
from Sunday evening.
Next, Joe needs to get the data that changed since Sunday.
Because Joe was using differential backups,
each differential backup contains all of the data changed
since the last full backup.
So Joe only needs to restore the most recent
differential backup, the one from Thursday evening.
But what if we change this question a bit,
and switched Joe's strategy from daily differential backups
to daily incremental backups?
Now Joe has a different situation on his hands.
Incremental backups are smaller than differential backups,
and contain only those files that have changed
since the most recent full or incremental backup.
So Joe begins the same way,
by restoring Sunday's full backup.
But then he must apply each incremental backup
in order that took place since the full backup.
This means that he must apply the incremental backups
from Monday, Tuesday, Wednesday and Thursday.
It takes a longer time to restore from incremental backups
because of this process.
But the trade off is that incremental backups
consume less space than differential backups.
As organizations perform backups,
they also need to develop plans for media rotation.
It's normally neither feasible nor desirable
to preserve every backup that the organization creates
on a permanent basis.
Backup rotation strategies describe how an organization
reuses backup media over time.
It's fairly uncommon to restore very old backups.
In most cases when an organization needs to restore data
from a backup, it's in the wake of a system failure
or user error.
These are usually noticed quickly and therefore,
most backup restoration requests involve
the most recent few days of backups.
Backup rotation strategies come in many different variations
but they all have the same intent.
They keep more copies of the most recent backups
and fewer copies of older backups.
Let's take a look at one common backup rotation strategy,
known as the grandfather-father-son or GFS approach.
In this approach the organization maintains
12 different sets of backup media,
four of them are designated as the son backup sets,
four are designated as the father backup sets
and four are designated as the grandfather backup sets.
Then as the organization performs its daily backups,
it follows a few rules.
On Mondays through Thursdays the organization
uses the son sets, on Monday it uses the first son set,
the second son set is for Tuesdays and so on.
The second rule is that every Friday the organization
uses the father sets.
These rotate so during the first week backups go
to father set one, then the next week they go to set two,
then set three and four the following weeks
before wrapping back around to set one again.
The final rule is that on the last day of the month,
regardless of what day of the week it is
the organization uses the grandfather set.
Let's take a quick look at how this works in action.
Let's say October 1st falls on a Monday,
the organization goes ahead and uses son set number one
which is always used on Mondays.
Tuesday son set number two is used,
then on Wednesday they use son set number three
and on Thursday, son set number four.
Then when Friday rolls around, our rule says that
we should go to the father set.
So we write the backups for that Friday to
father set number one.
Then when we return from the weekend, it's Monday again
and we go ahead and reuse son set number one,
son set number two, three and four.
That Friday on October 12th we use father set number two.
The next week we repeat the same process for the son set,
and use father set number three.
The following week we rotate again through the son set
and then we fill the last father set, number four.
Then as the last week of the month rolls around,
we begin by using son set number one
and son set number two,
but then on the last day of the month Wednesday October 31st
we rotate to the grandfather set
which contains backups from the last day of every month.
Once all of these sets have filled up,
we're left in a situation where we can go back in time
at different intervals.
We can restore backups from any of the past five days
from Friday of the past four weeks
and from the last day of the past four months.
We can do all of that with 12 sets of backup media.
Alternatively, if we had retained every day's backup media
from the past four months,
we'd have somewhere around 120 sets of tapes.
That's 10 times as expensive.
This is just one example of a backup rotation strategy.
Organizations can and do customize these schedules
to meet their unique business needs.
For example, one common twist on this
grandfather-father-son approach is to use
12 grandfather sets allowing the organization
to restore data from the last day of any month
within the past year.