Downloading and using PAR2 files from UseNetIn order to take full advantage of PAR2 files posted on UseNet, it is important to configure your newsreader to permit you to download incomplete files. PAR2 is still useable if your newsreader does not permit this, but you will need to download a greater quantity of PAR2 files than you would otherwise and repair will take considerably longer as a result. Reconstructing a whole file with PAR2 will always take longer than PAR1 would. Repairing a damaged file using PAR2 will very probably take less time than PAR1 would take to reconstruct it. When does using PAR 2.0 beat PAR 1.0?Using PAR2 files beats PAR1 files under any of the following circumstances:
Should PAR2 files be downloaded before, after or at the same time as data files?It is normally best to download files in the same order that they are uploaded. This will reduce the chance of individual files expiring before your newsreader makes the attempt to fetch them. As with PAR 1.0, posters should normally post the very small PAR2 file before the data files, and the other PAR2 files (which actually contain recovery data) after the data files. You should always download the smallest PAR2 file first (the one called "filename.ext.par2") since you can use this to verify the other files that you download. This works in exactly the same was as the small .PAR file for PAR 1.0. If you want, whilst the other files are being downloaded you can use the Monitor function to scan them as soon as they finish downloading. What should you download when you can see there are incomplete files before you start?With PAR 1.0 you would normally count the number of incomplete files and simply choose to download that number of PAR files. With PAR 2.0 you should instead count the number of articles that are missing, and you will probably require that number of recovery blocks. NB however that if the uploader has not matched the article size to the block size they used to create the PAR2 files, you might require up to two times as many recovery blocks as there are lost articles. If the posted PAR2 files have enough recovery blocks, then repair should be possible. QuickPar says I need NNN recovery blocks, what should I download?NB A "Recovery Block" and a "Recovery File" are NOT the same thing. If you are told you need 20 recovery blocks, then that does not mean you need to download 20 PAR2 files. PAR2 files normally contain more than 1 recovery block and the sizes of the PAR2 files vary in a way that makes it possible to download a combination that exactly matches the number of recovery blocks that you require. PAR2 files have names that take the following form: filename.ext.volFFF+NNN.par2 The number NNN tells you exactly how many recovery blocks are contained within the PAR2 file. An example of a set of PAR2 files would be:
If you were told that you needed 60 recovery blocks, you could either download two of the "+40" files (giving you 20 more blocks than you need), or one "+40" file and the "+28" file (giving you 8 more blocks than you need), or even one "+40" the "+15", "+04", and "+01" files (giving you exactly 60 recovery blocks). What to do if you have downloaded all incomplete files and all available PAR2 files but you are told you still need more recovery blocksAs with PAR 1.0, when this happens you can either ask for individual article fills, whole file reposts, or extra recovery blocks. It is recommended that you ask for more PAR2 files to be posted. It is extremely important when asking for additional PAR2 files that you specify exactly how many Recovery Blocks you need. If all you say is something like "please post 2 more PAR2 files" then the uploader won't know how many Recovery Blocks to post. |
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Peter B. Clements. All Rights Reserved. |