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# 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 REFFILE OUTFILE
> diff-dd restore [-s SECTOR_SIZE] [-b BUFFER_SIZE] INFILE OUTFILE
## Backup
Using ```diff-dd ``` for backup requires the full backup image to
exist. Differential backup is created with:
> diff-dd backup INFILE REFFILE OUTFILE
The ```INFILE``` is a path to the file to backup differentially, the
```REFFILE``` is the full image, and the ```OUTFILE``` is the file to
which only the changed sectors of the ```INFILE```, compared to the
```REFFILE```, and their offsets will be saved.
## Restore
The restoration means application of the changed sectors saved in the
```INFILE```, which is the differential image, to the ```OUTFILE```:
> diff-dd restore INFILE 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.
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