Backup types — full, differential, and incremental — differ in how much data they capture and how they handle restores. The archive bit flags changed files so backup software knows exactly what needs to be copied.
Backup Types Overview
There are different types of backups and they respond differently. Let's take a look at an overall picture of what some of these backup types look like.
This is a folder right here, and let's say this folder has a lot of different files in it, files that are being changed. Maybe this is 8:00 a.m., 9:00 a.m., 10, 11, 12 -- so this is a timeline of events here. What's going to happen is we want to take a backup of it.
Maybe we take a full backup of it. A full backup is pretty straightforward. We're just going to take all of this folder right here, take a capture of everything. It's great, because now if we want to do a restore, we can just restore everything. We've got a copy of everything.
The problem is that when you do a full backup it can take a long time, depending on how much data you're backing up. I've had backups where we started Friday night and it doesn't get done until Sunday afternoon, so it takes days in order to finish. This could be problematic. If I'm taking days and I need to do a backup every 15 minutes, that's problematic. I can't do that. So I might have to choose some other method, some other type, to back these up.
What are the other types? A couple of the types are differential or incremental. If you're doing a differential or incremental, it's not backing up everything -- it's just backing up the changes. That is what we're backing up with a differential and incremental.
How would backup software know which files and folders have been changed? There is an archive bit that tells it what has changed since the last backup. In this case right here, what we see is all the files within a folder, and we see a couple of files that have been changed, and when they are changed then the archive bit gets set. So it turns on, and that can track that this is something that needs to be backed up in the future.
I'm on a Windows machine, and let's see what this archive attribute actually looks like. What I'm going to do is right-click, say New, and we're going to create a new text document, and I'm just going to call this Archive Attribute.
This is a new document, right? So I'm going to take a look at the properties. The attribute section is right down here, so we're going to take a look at these attributes. In fact, the advanced attributes are just like switches -- they're turned on or off. We can see that file is ready for archiving. That means it's ready to be backed up, it's changed. The change is that it's new.
Let's say, though, that this is not new. Let's go ahead and click on that and uncheck it. Click OK, click OK again. And just to prove that we did change it, I'll open it up again, and we can see that this archive bit is turned off.
Next, I'm going to open it up. We're just going to type something in here. I'm going to close it and save it. Now let's see what happens to that archive bit. I'm going to go into Properties, Advanced, and now notice that the archive bit is set to on again. So what we've done is, when we make a change, this archive bit gets set to say okay, now you can actually back this up, because something has changed.
Databases have a similar mechanism, but instead of an archive bit that says yes, this is ready to archive, they have transaction logs. Those transaction logs are the new transactions that have happened, and they don't get rolled into the primary file until after certain types of backups.
Another area where choosing the right full, differential or incremental backup becomes really critical is when it goes to restoring. When we're copying these files, it can take a long time. Same thing with the restore process. But what could take even longer is if we have to restore multiple copies of something.
With a full backup you don't have to, because it's just all in one file -- it's just one full backup. But with differential and incremental, now we're breaking it up and we're taking chunks of data, and that could affect how many times we have to do a restore. So one thing to consider when we're choosing the right type of backup is, what does the restoration process look like?
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