What Backup Type Do I Want: Incremental or Differential?
HI everyone. Leo Notenboom here for askleo.com where I want to talk a little bit about these
three very confusing terms that a lot of backup programs will simply assume you know, and assume
you know what you want to choose. First let's talk about just backing up. A backup of anything is a
second copy. So for example, if you've got a file on your PC, then a backup of that file might be
a copy of that file on an external drive, or a copy of that file that's stored in the cloud.
The key concept there is that it's a copy. You have more than one copy of the file in more than
one place. That's a backup. Now when we talk about backing up your system well that means you'll take
a copy of your entire system and do something with it. You might take a copy of your entire system
and copy it to an external hard drive using backup software that does it all for you. Again the key
concept is you're making a copy of something in order to back it up. Now a full backup
is nothing more than a backup of everything you're referring to. When we talk about hard
disks or perhaps partitions it often is synonymous with an image backup,
but regardless, if you've got a folder a full backup of that folder is everything in it.
If you've got a system, a full backup of your system, is everything in the system.
That's your operating system your installed applications your data the overhead information.
It's a backup of everything. And that's a key component we'll end up coming back to.
If we've got a regularly occurring backup, a daily backup, and we're using full backups it's actually
pretty straightforward. If we start on Sunday then that Sunday backup will have a complete image
of the entire system as it was on Sunday. Come Monday we repeat the process with another full
backup. Which means it's a backup of the machine as it appeared on Monday. Same process on Tuesday
we take a full backup of the machine and we have a full copy of everything on that machine as it
existed on Tuesday. If you've kept all three you have three complete copies of the machine
as it appeared on these three different days. They're just big. They're going to be
proportional to the amount of data that was stored on the machine at the time you took the backup.
Now with space potentially being an issue we move on to what's called an incremental backup.
Incremental backups are so called because they work in increments compared to the previous
day. The best way again might be example. On Sunday we start our backups. An incremental backup
regimen always starts with a full backup. So on Sunday we create a full backup of our machine,
just like we did before. On Monday however things get different.
On Monday we back up only the files that have changed on Monday. That is a much smaller set
of files, and saves you a lot of space. You end up with the same information in that Sunday's backup,
the full image backup, represents the machine as it was on Sunday. But that full backup plus
the incremental backup that was taken on Monday represents the machine as it existed on Monday
on Tuesday. We repeat the process. We back up only those files that have changed since the previous
backup on Monday. Again presumably, a much smaller set. But once again on Tuesday we now have a
representation of the entire machine as it was on Tuesday. We used the full backup, the incremental
backup on Monday, and the incremental backup on Tuesday to gather all that information together.
That shows us what the machine was on Tuesday. So for incremental backup the summary is simply this:
the first backup Sunday in our example is a full backup of everything,
Monday's backup includes only those things that changed since Sunday, and Tuesday's backup
includes only those things that have changed since Monday. Together this collection of backups both
full and incremental can be used to restore the machine or gather any file on the machine from any
given date. Differential is less important because I actually don't recommend them in
general use. But for completeness: differential backups are kind of hybrid between the two.
Once again we'll start with our example and once again on Sunday the process starts with a complete
full backup. That doesn't change. On Monday we back up only those things that have changed
since Sunday. Again very much like an incremental backup. It's on Tuesday where everything changes.
On Tuesday we back up everything that has changed since Sunday. Since the starting backup
on Wednesday we would back up everything that changed between Sunday and Wednesday. And so
on. As you can see the difference is that a differential backup is backing up compared
to a starting point rather than compared to the previous day. So what do you want? I understand
the terms are confusing and perhaps they're still somewhat confusing. The good news here
is that you don't really need to understand them completely in order to make an intelligent choice.
My recommendation is simply this: that you set up your backup software to take a
full backup once a month, and then an incremental backup every day. That way every month you'll have
the opportunity to go back to any day within that month. Should you need to restore your system or
simply to recover a file I also recommend that you keep at least two months’ worth of your backups.
That way at the beginning of a month you still have the previous month's backups that you could
go back to throughout the month. The window only gets longer. You have the ability to,
at the end, go back anywhere between 30 and 60 days should you need to. Hopefully you never
need to. But that's the kind of safety net that I think gets you the most bang for your buck,
both in terms of complexity, disk space, and your ability to recover when you need to.
So in summary the terms are very very simple. Full is everything. Incremental is everything that's
changed since the last backup. And differential is everything that changed since the first backup.
Everything else we've talked about really just builds on those concepts. I hope this was helpful.
I understand that these are confusing terms. The companion article on which this video was based
goes into it in a little bit more detail and may be helpful in understanding the concepts even
further. You'll find that out at askleo.com/29760 along with links to related articles comments
updates and more. As always thank you for watching. I am Leo Notenboom this is askleo.com.