[compsciphd]

par2 is very limited.

It only support 32k parts in total (or in reality that means in practice 16k parts of source and 16k parts of parity).

Lets take 100GB of data (relatively large, but within realm of reason of what someone might want to protect), that means each part will be ~6MB in size. But you're thinking you also created 100GB of parity data (6MB*16384 parity parts) so you're well protected. You're wrong.

Now lets say one has 20000 random bit error over that 100GB. Not a lot of errors, but guess what, par will not be able to protect you (assuming those 20000 errors are spread over > 16384 blocks it precalculated in the source). so at the simplest level , 20KB of errors can be unrecoverable.

par2 was created for usenet when a) the size of binaries being posted wasn't so large b) the size of article parts being posted wasn't so large c) the error model they were trying to protect was whole articles not coming through or equivalently having errors. In the olden days of usenet binary posting you would see many "part repost requests", that basically disappeared with par (then quickly par2) introduction. It fails badly with many other error models.

[catlikesshrimp]

you can split files so you can have more par blocks (100GB in 100 1GB parts 32k blocks per part)

[compsciphd]

yes, but it just moves the needle a bit, if you lose 1 of the 1GB parts in totality, you also can't recover, so it really depends in on your error model you are trying to protect from.

In practice a DVD like PI/PO model would be the best for many people (protect the 1GB parts like you said with 5-10% redundancy, and then protect all 100 1GB parts together with 5-10% redundancy. the PI will repair as much as it can at the 1GB size, while the PO will be able to repair 1GB blocks that can't be repaired otherwise.

It be interesting if Par2 or something like it could implement it natively without people having to hack together their own one off solutions.

[e145bc455f1]

what other tool do you recommend?

[iberator]

just pay for storage instead. It's absurd that rich developers are doing ANYTHING but to pay for basic services - ruining the internet for those in real need.

we can't have nice things