5 ms·

For comparisons with PAR2, I had similar thoughts / concerns / notes, and note that the author of this has also factored PAR2 into their thinking: > Parchive (

For comparisons with PAR2, I had similar thoughts / concerns / notes, and note that the author of this has also factored PAR2 into their thinking: > Parchive (PAR1, PAR2, MultiPar): well known error correction file generator. The big advantage of Parchives is that an ecc block depends on multiple files: this allows to completely reconstruct a missing file from scratch using files that are still available. Works good for most people, but most available Parchive generators are not satisfiable for me because 1- they do not allow to generate an ecc for a directory tree recursively (except MultiPar, and even if it is allowed in the PAR2 specs), 2- they can be very slow to generate (even with multiprocessor extensions, because the galois field is over 2^16 instead of 2^8, which is very costly), 3- the spec is not very resilient to errors and tampering over the ecc file, as it assumes the ecc file won’t be corrupted (I also tested, it’s still a bit resilient, but it could be a lot more with some tweaking of the spec), 4- it doesn’t allow for partial recovery (recovering blocks that we can and pass the others that are unrecoverable): with PAR2, a file can be restored fully or it cannot be at all.

StavrosK 7y ago
It's too bad that one tool exists that's 99% of the way there, but for whatever reason someone writes a different tool for the extra 1%, and now you have a split user base.
- justin66 7y ago
  Do you think this would split the existing PAR user base, given that the pros don't matter much to those users (recursive directory blah blah... just create a zip file) and the cons (can't replace a missing file) matter a lot? It's an eccentric user base to begin with, of course. Most archivists and ordinary users just create multiple backups, and the file integrity concerns aside from file sharing and archiving are best addressed at the filesystem level.
  - StavrosK 7y ago
    I'm mostly referring to the choice between "using an unmaintained, less popular utility" vs "using the industry standards that lacks some useful features". It would obviously be nice if PAR were faster, for example.
pronoiac 7y ago
Re: corrupted ecc files - I have made par2 files covering other par2 files before, for irreplaceable data. I had, from memory here, md5sums of data, including in blocks of 64k or so; if the media failed, and I needed that data, I could picture a way to modify par2 software and piece together chunks from the par2 blocks.

StavrosK 7y ago

It's too bad that one tool exists that's 99% of the way there, but for whatever reason someone writes a different tool for the extra 1%, and now you have a split user base.

justin66 7y ago
Do you think this would split the existing PAR user base, given that the pros don't matter much to those users (recursive directory blah blah... just create a zip file) and the cons (can't replace a missing file) matter a lot? It's an eccentric user base to begin with, of course. Most archivists and ordinary users just create multiple backups, and the file integrity concerns aside from file sharing and archiving are best addressed at the filesystem level.
- StavrosK 7y ago
  I'm mostly referring to the choice between "using an unmaintained, less popular utility" vs "using the industry standards that lacks some useful features". It would obviously be nice if PAR were faster, for example.

pronoiac 7y ago

Re: corrupted ecc files - I have made par2 files covering other par2 files before, for irreplaceable data. I had, from memory here, md5sums of data, including in blocks of 64k or so; if the media failed, and I needed that data, I could picture a way to modify par2 software and piece together chunks from the par2 blocks.