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Creating Backups

## Backup Storage

In the backup destination folder, the program creates a folder dedicated to a particular backup project. The name of this folder is the project name plus an underscore symbol plus an alphanumeric prefix. For example, if your project is called "Documents", the folder name can look as Documents_4FFA23B7-207C-42BF-A9DB-A500023DD276. The prefix is generated automatically and ensures that projects with the same name will not mix up their backup folders.

Inside the backup folder, there are:

- gb3info.plist - an auxiliary file needed to store some information related to the backup.
- b3_2016-02-03_17-54-28 - a folder to store a version of backed up data. There can be one or many of such folders with different date and time in their names. Every time you run a backup project, the program creates one more folder, and copies the current version of your files into it.

If we look at the list of items included to the project, there are files and folders that are not inside of any other folder. Let's talk about them as top level items. So, the program places each top level item into a folder with the same name and a unique prefixes such as ".wrp1", ".wrp2" and so on. If you go deeper in subfolders, the file structure will be exactly the same as in the original folders.

So in the whole, the backup storage content may look this way:

Documents_4FFA23B7-207C-42BF-A9DB-A500023DD276
gb3info.plist
b3_2016-02-03_17-54-28
Document_1.txt.wrp1
Document_1.txt
Document_2.txt.wrp2
Document_2.txt
b3_2016-03-03_17-54-28
Document_1.txt.wrp1
Document_1.txt
Document_2.txt.wrp2
Document_2.txt
Folder_1.wrp3
Folder_1
Folder_2.wrp3
Folder_2
Document_3.txt
Document_4.txt

Bold font marks the backed up files and folders. The rest were used to organize the backup storage. To restore manually, you should copy the items in bold to the proper locations.

At the beginning of the backup process, a folder to store a new backup is named "GB3ProcessTemporaryFolder". When all files are successfully copied in this folder, the program gives it a proper name as explained earlier. If the process wasn't finished, the temporary folder remains until the next backup session. If files in the temporary folder are up-to-date, the program will not copy them again in the new session. This helps to finish the process faster.

#### Quasi-Incremental Backup Type

If the local destination drive has the APFS or Mac OS Extended file system, the program will create incremental backups. This means that files, which have not been changed since the previous backup, will not be copied to the backup storage again. Due to this, the program can save space on your destination drive, and may finish each backup session faster.

Instead of copying an unchanged file to a new backup, the program creates a hard link (feature of the file system) to a copy of this file already present in one of previous backups. So, there is no need to add another copy of the file and as a consequence take more disk space for it. To the user, the hard link behaves as it was the file itself. So, all backups appear to be full backups.

With a file system on the destination drive other than APFS or Mac OS Extended, hard links are not supported. In such case, the program will create full backups. Each of them will contain copies of all files included to the project.

Incremental backups cannot be created on network disks because hard links cannot be used.

To create an incremental backup on a disk that doesn't support hard links, you can choose to create a disk image on the selected storage when you set up a new backup project. The disk image will have a proper file system.

#### Using Disk Images

A disk image is a file (actually a bundle) that can be mounted as a volume in Finder. A disk image can have a file system that is different from one the physical storage has. Get Backup can use a disk image with the proper file system as a container to store your files.

The program mounts and unmounts disk images automatically when it backs up or restores files. Since disk images are fully supported by macOS, you can mount them manually in Finder and access your files without Get Backup.

Files and folders inside the disk image have the same structure as described at the beginning of this page.

In order to create a disk image to store your backup, you should select the Disk Image or Disk Image (Encrypted) option in the Properties dialog.

An encrypted disk image can be mounted only if the correct password is provided. If you want to backup your data automatically, you should allow the program to save the password to the Keychain.

An important property of disk images is the maximum size. When you create a new backup project, you should set an adequate maximum disk image size. For example, if your data takes 200 MB of disk space and you want to keep the last 5 full backups, the disk image size should be at least 1 GB that is 5 * 200 MB. You should add extra 10-20% to this estimate to be sure that your files will fit.

The initial size of a new disk image is about 5% of the maximum or less. When files are added to the disk image, it becomes larger to accomodate new files. The disk image will grow up until it reaches the maximum size. When it is not enough space to complete the task, the program will offer you to increase the maximum size of the existing disk image, or create a bigger one.

If you delete some files from a disk image, it will not shrink itself. The program cannot free unused disk space. You can only do this using the following Terminal command:
`hdiutil compact`

To run this command, open Applications/Utilities/Terminal.app. Copy and paste the command above. Then drag the disk image from Finder and drop it onto the Terminal window. Then hit the Return key. Note that there must be a space symbol between "compact" and the path to the disk image. If the disk image is encrypted, you will be asked to input the password. If you unsure how to use Terminal, don't use it. Most of actions that can be performed in Terminal have no UNDO function.

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