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**!! This is a Pre-alpha version. Expect changes and bugs. !!**

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![Status of the tests for the master branch](https://github.com/jansucan/diff-dd/actions/workflows/tests.yml/badge.svg?branch=master)

# diff-dd

This simple utility was created to reduce size of backup images of disk
partitions. It is intended to be used in conjunction with ```dd``` or similar
utility. The primary concern is safe operation, so ```diff-dd``` performs many
checks of the input and output files. For example, the differential image file
is read twice when restoring it. Because of that, it is slower.

## Synopsis

> diff-dd help

> diff-dd backup [-s SECTOR_SIZE] [-b BUFFER_SIZE] INFILE BASEFILE OUTFILE

> diff-dd restore [-s SECTOR_SIZE] [-b BUFFER_SIZE] DIFFFILE OUTFILE

## Backup

Using ```diff-dd ``` for backup requires the full backup image to
exist. Differential backup is created with:

> diff-dd backup INFILE BASEFILE OUTFILE

The ```INFILE``` is a path to the file to backup differentially, the
```BASEFILE``` is the full image, and the ```OUTFILE``` is the file to
which only the changed sectors of the ```INFILE```, compared to the
```BASEFILE```, and their offsets will be saved.

## Restore

The restoration means application of the changed sectors saved in the
```DIFFFILE```, which is the differential image, to the ```OUTFILE```:

> diff-dd restore DIFFFILE OUTFILE

## Options

```-s``` sets the sector size by which the files will be processed
(default is 512 B). It can be used to control granularity of
differential backup.

```-b``` sets the size of the buffer for the sectors of the input and
output file (default is 4 MiB). The input data is always buffered. The
output data are buffered only in backup mode.

## Example

First, the full image of the partition to backup has to be created:

> dd bs=4M if=/dev/sda1 of=full.img

When the user decides to create the differential image, he or she runs:

> diff-dd backup /dev/sda1 full.img diff.img

If a data accident happens, the partition can be restored by running:

> dd bs=4M if=full.img of=/dev/sda1

> diff-dd restore diff.img /dev/sda1

The first command restores the old full image. The second one applies
the differences.