Thread: Differential vs Incremental Backup

Sure - an incremental backup is a rolling backup since the last full backup, whereas a differential backup is an accumulative backup since the last full backup.

Consider the following scenario.

INCREMENTAL:
Sunday: A full backup is made of the computer. Every file is copied.
Monday: Only files changed since Sunday are copied.
Tuesday: Only files changed since Monday are copied.
Wednesday: Only files changed since Tuesday are copied.
etc, etc.

DIFFERENTIAL:
Sunday: A full backup is made of the computer. Every file is copied.
Monday: All files changed since Sunday are copied.
Tuesday: All files changed since Sunday are copied.
Wednesday: All files changed since Sunday are copied.
etc, etc.

The advantages of incremental backups are that they consume minimum storage space and are quicker to perform than differential backups. However the restoration process can take longer as it would need the last full backup plus all the incremental backups until the point-in-time of the restoration.

Conversely, with differential backups, as time goes by the backup process takes longer and longer, as more and more files have changed since the initial full backup. However the restoration process is much more straightforward, as all that is needed is the last full backup, plus the last differential backup to restore the system.

what are you planning to back up?

this will make a difference to the type of backup you need

Originally Posted by mike_ie

INCREMENTAL:
Sunday: A full backup is made of the computer. Every file is copied.
Monday: Only files changed since Sunday are copied.
Tuesday: Only files changed since Monday are copied.
Wednesday: Only files changed since Tuesday are copied.
etc, etc.

DIFFERENTIAL:
Sunday: A full backup is made of the computer. Every file is copied.
Monday: All files changed since Sunday are copied.
Tuesday: All files changed since Sunday are copied.
Wednesday: All files changed since Sunday are copied.
etc, etc.

OK. thanks, the penny has dropped, for differential backup the base for comparison is always the initial backup, for incremental backups the base for comparison is always the last incremental backup.

Another question then.

Lets say I do daily backups and I only ever need to restore from one of the last 3 'versions' of any file or partition.

With differential backup I can see I need only keep the initial full backup + the last 2 differential backup copies. Older differential backups can just be deleted.

How is this accomplished if incremental backup is used? I can only think of one way of doing this - since the older increments can't be deleted they must somehow be merged into the initial full backup, keeping the last two incremental backups only. This would take some of the shine off the speed advantage of a incremental backup.

Whether you are using Incremental or Differential backups, you still make a full backup of the drive, say every week or every month. If you want to achieve what you are looking for from incremental backup software, you set the software to do a full backup every four days, and an incremental backup on the other three.

Maybe there is fancier backup software than can pull what you want from a stack of incremental backups, but the above scenario has been my experience. And if this is the setup you want, then I'd probably use a differential backup for granularity and ease, unless what your backing up is huge, and storage space is at a premium.

Originally Posted by Eevo

what are you planning to back up?

this will make a difference to the type of backup you need

Usual setup. Drive C: with just the OS and Drive D: with applications and data.

Problem is, there are some applications which refuse to install in anything other than drive C: and there are some which install mostly in drive D: but still have a presence in C: as well.

So there is no real clear divide between the OS partition and the application / data partition.

In the past I have just backed up 'data' only using simple file sync methods with the intention of just re installing the OS and applications if needed. But I have so many applications now I just don't want to face the prospect of reinstalling every thing from scratch, customising each again.

That's the motivation for looking at and understanding more complex backup solutions at the moment.

Honestly, you'd probably make things far easier on yourself if you loaded your OS and applications onto Drive C, and used drive D solely for data, even if you have to go out and buy a bigger drive to be your C: drive.

As you've discovered, there is much overlap between the two drives, and SOP in this case would be to separate the data completely from the OS and the data's associated application.

It also makes backups far more straightforward too - you can run a systems backup, say, once a month (drive C: ), and run a data backup (Drive D: ) every night if you wish.

Originally Posted by mike_ie

Honestly, you'd probably make things far easier on yourself if you loaded your OS and applications onto Drive C, and used drive D solely for data, even if you have to go out and buy a bigger drive to be your C: drive.

As you've discovered, there is much overlap between the two drives, and SOP in this case would be to separate the data completely from the OS and the data's associated application.

It also makes backups far more straightforward too - you can run a systems backup, say, once a month (drive C: ), and run a data backup (Drive D: ) every night if you wish.

exactly

my main computer

c: OS n apps (250gb)
e: tv shows (3t
f: movies (3tb)
g: music, games, doco's, (2tb)
h: porn (1tb)

What operating system are you using? The incremental/ differntial debate is very important with XP, but the standard OS driven backups in W7 can be handled a bit differently.