Comparing Backup Types
Backup utilities support several different types of backups. Even though third-party backup
programs can be quite sophisticated in what they do and how they do it, you should have a solid
understanding of the basics.
The most common media used for backups is tape. Tapes store more data and are cheaper than
other media, though some organizations use hard disk drives for backups. However, the type of media doesn’t affect the backup type.
The following backup types are the most common:
Full backup. A full (or normal backup) backs up all the selected data.
Differential backup. This backs up all the data that has changed or is different since the last
full backup.
Incremental backup. This backs up all the data that has changed since the last full or incremental backup.
Full Backups
A full backup backs up all data specified in the backup. For example, you could have several
folders on the D: drive. If you specify these folders in the backup program, the backup program backs
up all the data in these folders.
Although it’s possible to do a full backup on a daily basis, it’s rare to do so in most production
requirements. This is because of two limiting factors:
Time. A full backup can take several hours to complete and can interfere with operations.
However, administrators don’t always have unlimited time to do backups and other system
maintenance. For example, if a system is online 24/7, administrators may need to limit the
amount of time for full backups to early Sunday morning to minimize the impact on users.
Money. Backups need to be stored on some type of media, such as tape or hard drives.
Performing full backups every day requires more media, and the cost can be prohibitive.
Instead, organizations often combine full backups with differential or incremental backups.
However, every backup strategy must start with a full backup.
Restoring a Full Backup
A full backup is the easiest and quickest to restore. You only need to restore the single full
backup and you’re done. If you store backups on tapes, you only need to restore a single tape.
However, most organizations need to balance time and money and use either a full/differential or a
full/incremental backup strategy.
Differential Backups
A differential backup strategy starts with a full backup. After the full backup, differential
backups back up data that has changed or is different since the last full backup.
For example, a full/differential strategy could start with a full backup on Sunday night. On
Monday night, a differential backup would back up all files that changed since the last full backup on
Sunday. On Tuesday night, the differential backup would again back up all the files that changed since the last full backup. This repeats until Sunday, when another full backup starts the process again. As the week progresses, the differential backup steadily grows in size.
Restoring a Full/Differential Backup Set
Assume for a moment that each of the backups was stored on different tapes. If the system
crashed on Wednesday morning, how many tapes would you need to recover the data?
The answer is two. You would first recover the full backup from Sunday. Because the
differential backup on Tuesday night includes all the files that changed after the last full backup, you
would restore that tape to restore all the changes up to Tuesday night.
Incremental Backups
An incremental backup strategy also starts with a full backup. After the full backup, incremental
backups then back up data that has changed since the last backup. This includes either the last full
backup, or the last incremental backup.
As an example, a full/incremental strategy could start with a full backup on Sunday night. On
Monday night, an incremental backup would back up all the files that changed since the last full
backup. On Tuesday night, the incremental backup would back up all the files that changed since the
incremental backup on Monday night. Similarly, the Wednesday night backup would back up all files
that changed since the last incremental backup on Tuesday night. This repeats until Sunday when
another full backup starts the process again. As the week progresses, the incremental backups stay
about the same size.
Restoring a Full/Incremental Backup Set
Assume for a moment that each of the backups was stored on a different tape. If the system
crashed on Thursday morning, how many tapes would you need to recover the data?
The answer is four. You would first need to recover the full backup from Sunday. Because the
incremental backups would be backing up different data each day of the week, each of the incremental backups must be restored and in the chronological order.
Sometimes, people mistakenly think the last incremental backup would have all the relevant
data. Although it might have some relevant data, it doesn’t have everything.
As an example, imagine you worked on a single project file each day of the week, and the system
crashed on Thursday morning. In this scenario, the last incremental backup would hold the most
recent copy of this file. However, what if you compiled a report every Monday but didn’t touch it
again until the following Monday? Only the incremental backup from Monday would include the most recent copy. An incremental backup from Wednesday night or another day of the week wouldn’t include the report.
Choosing Full/Incremental or Full/Differential
A logical question is, “Why are there so many choices for backups?” The answer is that different
organizations have different needs.
For example, imagine two organizations perform daily backups to minimize losses. They each
do a full backup on Sunday, but are now trying to determine if they should use a full/incremental or a
full/differential strategy.
The first organization doesn’t have much time to perform maintenance throughout the week. In
this case, the backup administrator needs to minimize the amount of time required to complete
backups during the week. An incremental backup only backs up the data that has changed since the
last backup. In other words, it includes changes only from a single day. In contrast, a differential
backup includes all the changes since the last full backup. Backing up the changes from a single day
takes less time than backing up changes from multiple days, so a full/incremental backup is the best
choice.
In the second organization, recovery of failed systems is more important. If a failure requires
restoring data, they want to minimize the amount of time needed to restore the data. A full/differential is the best choice in this situation because it only requires the restoration of two backups, the full and the most recent differential backup. In contrast, a full/incremental can require the restoration of several different backups, depending on when the failure occurs.
Remember this
If you have unlimited time and money, the full backup alone provides the
fastest recovery time. Full/incremental strategies reduce the amount of time
needed to perform backups. Full/differential strategies reduce the amount of
time needed to restore backups.
Testing Backups
I’ve heard many horror stories in which personnel are regularly performing backups thinking all
is well. Ultimately, something happens and they need to restore some data. Unfortunately, they
discover that none of the backups holds valid data. People have been going through the motions, but
something in the process is flawed.
The only way to validate a backup is to perform a test restore. Performing a test restore is
nothing more than restoring the data from a backup and verifying its integrity. If you want to verify that
you can restore the entire backup, you perform a full restore of the backup. If you want to verify that
you can restore individual files, you perform a test restore of individual files. It’s common to restore
data to a different location other than the original source location, but in such a way that you can
validate the data.
As a simple example, an administrator can retrieve a random backup and attempt to restore it.
There are two possible outcomes of this test, and both are good:
The test succeeds. Excellent! You know that the backup process works. You don’t
necessarily know that every backup tape is valid, but at least you know that the process is
sound and at least some of your backups work.
The test fails. Excellent! You know there’s a problem that you can fix before a crisis. If you
discovered the problem after you actually lost data, it wouldn’t help you restore the data.
An additional benefit of performing regular test restores is that it allows administrators to
become familiar with the process. The first time they do a restore shouldn’t be in the middle of a
crisis with several high-level managers peering over their shoulders.
Source:- Darril Gibson
Backup utilities support several different types of backups. Even though third-party backup
programs can be quite sophisticated in what they do and how they do it, you should have a solid
understanding of the basics.
The most common media used for backups is tape. Tapes store more data and are cheaper than
other media, though some organizations use hard disk drives for backups. However, the type of media doesn’t affect the backup type.
The following backup types are the most common:
Full backup. A full (or normal backup) backs up all the selected data.
Differential backup. This backs up all the data that has changed or is different since the last
full backup.
Incremental backup. This backs up all the data that has changed since the last full or incremental backup.
Full Backups
A full backup backs up all data specified in the backup. For example, you could have several
folders on the D: drive. If you specify these folders in the backup program, the backup program backs
up all the data in these folders.
Although it’s possible to do a full backup on a daily basis, it’s rare to do so in most production
requirements. This is because of two limiting factors:
Time. A full backup can take several hours to complete and can interfere with operations.
However, administrators don’t always have unlimited time to do backups and other system
maintenance. For example, if a system is online 24/7, administrators may need to limit the
amount of time for full backups to early Sunday morning to minimize the impact on users.
Money. Backups need to be stored on some type of media, such as tape or hard drives.
Performing full backups every day requires more media, and the cost can be prohibitive.
Instead, organizations often combine full backups with differential or incremental backups.
However, every backup strategy must start with a full backup.
Restoring a Full Backup
A full backup is the easiest and quickest to restore. You only need to restore the single full
backup and you’re done. If you store backups on tapes, you only need to restore a single tape.
However, most organizations need to balance time and money and use either a full/differential or a
full/incremental backup strategy.
Differential Backups
A differential backup strategy starts with a full backup. After the full backup, differential
backups back up data that has changed or is different since the last full backup.
For example, a full/differential strategy could start with a full backup on Sunday night. On
Monday night, a differential backup would back up all files that changed since the last full backup on
Sunday. On Tuesday night, the differential backup would again back up all the files that changed since the last full backup. This repeats until Sunday, when another full backup starts the process again. As the week progresses, the differential backup steadily grows in size.
Restoring a Full/Differential Backup Set
Assume for a moment that each of the backups was stored on different tapes. If the system
crashed on Wednesday morning, how many tapes would you need to recover the data?
The answer is two. You would first recover the full backup from Sunday. Because the
differential backup on Tuesday night includes all the files that changed after the last full backup, you
would restore that tape to restore all the changes up to Tuesday night.
Incremental Backups
An incremental backup strategy also starts with a full backup. After the full backup, incremental
backups then back up data that has changed since the last backup. This includes either the last full
backup, or the last incremental backup.
As an example, a full/incremental strategy could start with a full backup on Sunday night. On
Monday night, an incremental backup would back up all the files that changed since the last full
backup. On Tuesday night, the incremental backup would back up all the files that changed since the
incremental backup on Monday night. Similarly, the Wednesday night backup would back up all files
that changed since the last incremental backup on Tuesday night. This repeats until Sunday when
another full backup starts the process again. As the week progresses, the incremental backups stay
about the same size.
Restoring a Full/Incremental Backup Set
Assume for a moment that each of the backups was stored on a different tape. If the system
crashed on Thursday morning, how many tapes would you need to recover the data?
The answer is four. You would first need to recover the full backup from Sunday. Because the
incremental backups would be backing up different data each day of the week, each of the incremental backups must be restored and in the chronological order.
Sometimes, people mistakenly think the last incremental backup would have all the relevant
data. Although it might have some relevant data, it doesn’t have everything.
As an example, imagine you worked on a single project file each day of the week, and the system
crashed on Thursday morning. In this scenario, the last incremental backup would hold the most
recent copy of this file. However, what if you compiled a report every Monday but didn’t touch it
again until the following Monday? Only the incremental backup from Monday would include the most recent copy. An incremental backup from Wednesday night or another day of the week wouldn’t include the report.
Choosing Full/Incremental or Full/Differential
A logical question is, “Why are there so many choices for backups?” The answer is that different
organizations have different needs.
For example, imagine two organizations perform daily backups to minimize losses. They each
do a full backup on Sunday, but are now trying to determine if they should use a full/incremental or a
full/differential strategy.
The first organization doesn’t have much time to perform maintenance throughout the week. In
this case, the backup administrator needs to minimize the amount of time required to complete
backups during the week. An incremental backup only backs up the data that has changed since the
last backup. In other words, it includes changes only from a single day. In contrast, a differential
backup includes all the changes since the last full backup. Backing up the changes from a single day
takes less time than backing up changes from multiple days, so a full/incremental backup is the best
choice.
In the second organization, recovery of failed systems is more important. If a failure requires
restoring data, they want to minimize the amount of time needed to restore the data. A full/differential is the best choice in this situation because it only requires the restoration of two backups, the full and the most recent differential backup. In contrast, a full/incremental can require the restoration of several different backups, depending on when the failure occurs.
Remember this
If you have unlimited time and money, the full backup alone provides the
fastest recovery time. Full/incremental strategies reduce the amount of time
needed to perform backups. Full/differential strategies reduce the amount of
time needed to restore backups.
Testing Backups
I’ve heard many horror stories in which personnel are regularly performing backups thinking all
is well. Ultimately, something happens and they need to restore some data. Unfortunately, they
discover that none of the backups holds valid data. People have been going through the motions, but
something in the process is flawed.
The only way to validate a backup is to perform a test restore. Performing a test restore is
nothing more than restoring the data from a backup and verifying its integrity. If you want to verify that
you can restore the entire backup, you perform a full restore of the backup. If you want to verify that
you can restore individual files, you perform a test restore of individual files. It’s common to restore
data to a different location other than the original source location, but in such a way that you can
validate the data.
As a simple example, an administrator can retrieve a random backup and attempt to restore it.
There are two possible outcomes of this test, and both are good:
The test succeeds. Excellent! You know that the backup process works. You don’t
necessarily know that every backup tape is valid, but at least you know that the process is
sound and at least some of your backups work.
The test fails. Excellent! You know there’s a problem that you can fix before a crisis. If you
discovered the problem after you actually lost data, it wouldn’t help you restore the data.
An additional benefit of performing regular test restores is that it allows administrators to
become familiar with the process. The first time they do a restore shouldn’t be in the middle of a
crisis with several high-level managers peering over their shoulders.
Source:- Darril Gibson
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