Using 7-zip and batch files to perform backups automatically

UPDATE: I have recently overhauled this and created a simpler script in this post: /2009/10/17/simpler-version-of-the-7-zip-backup/

First, a little history:

Since the days when I started using XP I had gotten used to the control that NT Backup provided to allow me to backup my files.

About a year ago I moved to Vista and was unhappy with the “All or nothing” approach that the bundled backup software provided. I was also using OneCare at the time and it followed a similar policy.

Since moving to BitDefender I was much happier with the backup software it provided yet the fact that I was not using a well known backup format rubbed me.

So, using this article: http://www.wilshireone.com/article/115/easy-backups-with-7-zip as a guide, I engineered my own backup mechnism using 7-zip.

Now heres the fun. My backup schedule consists of a weekly incremental backup and one monthly full backup. My files are not so important that I need frequent backups, this schedule suits me down to the ground.

My solution consists of 7 parts:

  • Backup.cmd, this is the main script that executes the command
  • Backupset.txt, a list of files and folders that I wish to backup
  • CurrentSet.txt, a path to the current backup file. Used by incremental backups to update
  • FullBackup.cmd, the script to run a full backup
  • FullBackupSettings.ini, the settings used by a full backup
  • IncrementalBackup.cmd, the script to run an incremental backup
  • IncrementalBackupSettings.ini, the settings used by the incremental backup

Now you could remove the separate scripts for the full and incremental backup, the reason I created separate scripts was that I don”t have to change the arguments in the task scheduler. Instead it is all controlled through those scripts.

Backup.cmd

The backup script loads the settings passed as argument 1, does some checking, then calls 7-zip to begin backing up. The settings files define how the files are added and where to etc.

BackupSet.txt

This is the list file passed to 7-zip. The only downside is that you cannot list the same folder or file name twice in this file. The work around would be to invoke multiple backup scripts and then add the duplicate folders and nested zips.

CurrentSet.txt

This contains the backup file created in the last full backup. Incremental backups then read it in and use it to update files.

FullBackup.cmd

Simples, it just calls the main backup script with the correct settings.

FullBackupSettings.ini

The settings file is read in and used in the main backup script. Note the mode and backup type, this is what separates the two types of backup.

IncrementalBackup.cmd

Similar to the full version, except its providing the increment backup settings

IncrementalBackupSettings.ini

Similar to the full settings, but with the zip mode set to update and its backup type defined as incremental.

Once that has all been put in place, all I do is create two tasks in the windows task scheduler.

You could go one step further and have the script copy the backups to another disk, I just do this myself when I feel like.

Update

After a little testing I found a flaw in the technique that I was using. Essentially what is happening is that new files are being added to the old archive and any deleted files were being left. I want to keep any files that I deleted but I do not want them muddying up the actual latest image.

Instead, what I did was use the -u switch to stop updates to the base archive being made and adding new files to a new archive, which makes it incremental in its true sense.

Backup.cmd

In fact, I have gone one step further and I have built a command line tool that wraps 7-zip and provides a nicer mechanism for configuring the backups. It then executes 7-zip. Once I have tested it a little I will post the source code.

Leave a Reply