bitrot_(par2).md

Managing BitRot with Parchive (Par2)

Parchive is an erasure code system which produces par files for data integrity verification with the ability to recover / repair corrupted and missing data.

Install par2cmdline

Debian

$ sudo apt install par2

Generic

$ git clone https://github.com/Parchive/par2cmdline
$ cd par2cmdline
$ ./automake.sh
$ ./configure
$ make
$ make check
$ make install

Creating par2 files

• -n1 : Only create 1 par2 file (besides index).
• -r5 : Create redundancy of 5%. Set higher if file importance is higher.

$ par2 c -n1 -r5 <file>

$ find <path> -type f -not -name "*.par2" -exec par2 c -n1 -r5 {} \;

Verify file

$ par2 v <file>.par2

$ find <path> -type f -name "*.par2" -exec par2 v {} \;

Repair file

$ par2 r <file>.par2

Creating a par2 directory

Create the par2 files

$ find <path> -type f -not -name "*.par2" -exec par2 c -n1 -r5 {} \;

Move to par2 directory

$ rsync -avR --remove-source-files --include="*.par2" --exclude="par2/" --include="*/" --exclude="*" <basepath>/ <basepath>/par2/

Verify from par2 directory

Run in base directory with par2 directory.

#!/bin/bash

IFS=$'\n'
for x in $(find "par2" -type f -name "*.par2")
do
    par2 v -q -B "$(dirname "${x#par2/}")" "${x}"
done