Background
We all know that data backup is important.  Hard drives can and do fail, potentially losing forever data that we do NOT want to lose.  As drives become larger, backing up valuable data become more time consuming and complicated.  Some data changes frequently and, if lost, can be painful.  It would be nice if we could go back in time and recover that file.

When data was on drives that were measured in kilo bytes, or even mega bytes, a copy to another drive was a simple way to backup.  Multiple versions were not available, but it was always possible to drop back to an older version, which was better than nothing.  Now, we have drives that are measured in gigabytes and terabytes. A simple copy can take hours, or in the case of multi-terabyte drives, days!  Backup technology and timing has become much more difficult and complicated.

Types
Considering the types of backups, the simplest and possibly least useful is the simple copy.  It is time consuming, and, if you are backing up bad data, once the backup is made, you no longer have access to good data.

There is a bit image backup that copies the entire structure of you drive to a special format that can be recovered in it's entirety.  It shares the same drawbacks as the simple copy, but it is very useful for system drives, as they can be recovered with the operating system intact, and usually can be accessed via a boot CD for disaster recovery when you cannot even boot the computer.  Everyone should have at least one copy of the operating system disk and a recovery CD.

There are three major types of backup: Full, Differential, and incremental.

A full backup is a copy of the entire drive.  It is a snap shot in time.  Any sound backup routine begins with a full backup

The differential backup is based on the full backup and is a copy of all of the files that have changed since the last full backup.  There are two data sets, the full and all that has changes since the full was made.  Crude, yet simple to make and maintain.  As changes become significant, a new full backup is made, and the cycle continues.

The incremental backup, starts with a full backup, and creates a new data set each time it is run that contains only files that have changes since the last full or incremental backup.  This is fast and offers reasonable version access, though finding the data set that contains the latest file desired can be difficult.  Most systems that offer incremental backups also offer some form of version control.  When versions become too numerous, a new full backup can be taken and the cycle can begin again.

There is a backup technique that is a hybrid of the above techniques and offers the best of all worlds.  This is a version control backup.  A full backup is made, and subsequent backups examine only changed or deleted files, copy over or delete them AND make a backup of the old file in a special version control library where the user can specify number of copies and the retention period.

Implementation
To insure reasonable data integrity, an external drive of sufficient capacity should be used.  The backup should be automated during hours when the computer is normally on so that it is not “forgotten”.  The same drive can be used to hold an image backup of the system drive.  It is fairly easy to configure multiple backups to share the same drive.

Be aware that multiple drives can exist on one physical drive.  This is called partitioning.  Just because you can see a “C” and “D” drive does not mean that you really have two physical drives in your machine.  Backing up “C” to “D” may sound like a good idea, but if they are the same physical drive, a problem on one could make the other inaccessible.  This is why an external drive is so important.

If you go one a trip, you can take the drive with you, insuring that, even if a total disaster happens to your home, you still have your data.

Considerations
I do not recommend “cloud” services.  I've known those services to “lose” data and I have a problem with NSA, and who knows who else, having access to my private data.  Also, if you have many terabytes of data, the load time to a cloud service will be prohibitive and may max out your ISP contract caps.  Most of us DO have them, even if we don't know it.

Investigate the external drives available and select a size, not less than a terabyte, that is appropriate to you and your life stye, and DO IT YOURSELF.

If you are truly paranoid, you'll get two devices, fully encrypt one, and mirror the first to the second every week or so, and put the second somewhere where it is not subject to any home disasters, like the trunk of your car.  Of  course, that won't be current, but if the worst were to happen, it would beat nothing.

For most people, that is over kill, but you should consider eventualities and evaluate the level of risk you are will to take against the difficult of implementing procedures to protect against it.

If you don't have backup procedures in place, NOW is the time to start!