CDNWiki - View Source: PAR2

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Using PAR2 to generate parity information to use up the remaining space on a CD or DVD, to increase chances of recovering from minor discrot or scratches

A DVD has 2295104 2048-byte sectors. Expect to use around 2-4MB for the ISO/Joliet/Rock Ridge filesystem structures. More, if you have a ton of small files.

Usable data space is, roughly, 4,696,178,688 bytes.

I choose a parchive block size of 262144 bytes (256kB) to keep the block count low, and to keep the block size a multiple of a DVD or CD ECC group size (32kB) to minimize wasted space.

* Collect the byte counts of the subsets to protect.
* Compute the amount of free space remaining after all the subsets are accounted for.
* Compute the percentage of each subset to the total amount used.
* Split the free space amongst the subsets, so that each gets a quantity in relation to its percentage.
* Compute the number of blocks each subset requires for parchive information.
* Compute the parchive information for each subset.
** par2 create -s262144 -c<parblks> -n1 -v -v <filename>.par2 <glob> <- Note the lack of spaces in parameters. It hates the spaces.
* After computing all parchive info (you can remove non-parity par2 files), make the iso9660 filesystem
** mkisofs -o image.iso -v -v -iso-level 4 -J -r -p 'CyberLeo' -V 'Image01' 01/