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GUIDE: How to Repair an Archive with PAR2 Files

MCP

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Usenet is far superior in terms of storage and speed. You can usually download an 8GB file in 2 hours or less depending on your ISP's speed. Another added bonus is that for paid premium subscribers file retention is generally three years or more. This is great what with the unreliable nature of bittorrent and digital lockers.

But with this superior platform there is the potential of files missing "segments". (Think of the RAR file being a wall and the segments being the bricks that make up the wall.) This is because, unlike digital lockers, usenet servers share all posts amongst each other; there is no centralize location. A missing segment can be a headache since it can prevent an archive from decompressing.

That's where PAR2 files come in. If you download files from usenet they most likely will come with several PAR2 files. These files are basically an insurance: if a segment is missing these PAR2 files can patch the segment and allow the archive to decompress properly.

The process is pretty painless and only requires one program. Uploaders use this program to create the PAR2 files, and end users can use it to repair broken files. Here is how you can repair a broken archive downloaded from usenet.

Requirements:
MultiPar
Archive with PAR2 files (labeled like ".vol000+004.par2", ".vol004+007", etc.)


  1. Start MultiPar. In the bottom left corner of the program is a button labeled Open. Click this and navigate to where you downloaded the files. Choose the .PAR2 file and click Open.
  2. MultiPar will now verify your PAR2 files, and then it will scan your RAR files. Once it's done it should tell you how many more blocks are needed. Fear not! If you have all the PAR2 then the Repair button should be clickable. Click it.
  3. QuickPar will now repair the archive and you should be good to go!

NOTE: Some usenet downloaders (SABnzbd, etc.) automatically have repair options enabled. The problem is that these programs delete the repair PAR2 files even if they unsuccessfully repair the files. It is best to disable automatic repairs using these program and do it manually.
 

geminigod

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I just encountered a scenario with one of l8wrtr's edits where the repair function didn't accomplish anything. I am still very new at this, so the following hypothesis as to why might be wrong, but I am guessing it had to do with the fact that the RAR file segments were split into 200MB segments instead of 50 MB segments, per the details in your uploading to usenet guide.
 

Q2

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geminigod said:
I just encountered a scenario with one of l8wrtr's edits where the repair function didn't accomplish anything. I am still very new at this, so the following hypothesis as to why might be wrong, but I am guessing it had to do with the fact that the RAR file segments were split into 200MB segments instead of 50 MB segments, per the details in your uploading to usenet guide.

I do 200MB segments too when working with larger files. I think I said 50MB for 1000MB or less. Don't remember though.
 

Neglify

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I personally found that when using 200MB files to upload to Usenet I was getting more corrupted files. It may be because of my internet connection, but when I do 50MB I'll get maybe only 1 corrupted file at most. It still sucks to have that corrupted file but 1 part missing is better than 19 parts missing.
 

Q2

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I've never had that many parts missing. I think at most was two segments in two separate RAR files. I just re-uploaded those missing segments and all was good.
 

geminigod

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I think this may shed some light on the matter.

http://www.binaries4all.com/optimizing/

I am still not 100% certain that size of rar file doesn't matter. It seems logical that larger file sizes might have increased chance of data loss or corruption as they bounce around servers. The largest example used on that link is ~50MB (ideally 49.92MB).

I'll try to recap the math here:
yenc line (which is the actual binary coding language) = 128 characters.
max allowed lines per segment = 5000 lines
So 1 segment = 128*5000 = 640,000 bytes

RAR files should be a multiple of this. So theoretically we could do a RAR file that is 310 segments * 640,000 bytes = 198,400,000 bytes.

Then in multiPAR we set the PAR2 block size to equal the segment size of 640,000 bytes so that repair is optimized.
 

geminigod

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Case and point, Q2, I just finished downloading your BD of episode 2 using SABnzbd. Repair took forever. Ultimately it failed against SFV verification saying it was 2 repair blocks short. Your file sizes were 204,800 KB. Repair took forever. 10 PAR2 repair files were created.

20 gigs and $2 later, I'm not sure what to do now as far as whether this download is salvageable or not. Same issue I had with L8wrtr's Episode 1 BD.

EDIT: Success. When all was said and done after my newsreader failed to repair, I clicked on the small par2 index file (as multiple guides have indicated) and multipar app examined the download. It stated that 2 slices/articles/segments or whatever the fuck you want to call them were missing. It also said that the large par2 repair files were "useless". Clicking the repair button did nothing. So I exited multipar, read this: http://www.slyck.com/Newsgroups_Guide_PAR_PAR2_Files, and then clicked on one of the large par2 repair files that my newsreader had put together. That opened multipar back up and suddenly it was magically fixed. {Head scratch... shrug... WTF}
 

Q2

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Good to know Gemini. Thanks for sharing!
 

Dethryl

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I'm having an issue that could hopefully be helped. The CRC check fails in SABnzbd and I also get the following errors when using WinRAR.

! BD25.part023.rar: Packed data CRC failed in \BDMV\STREAM\00005.m2ts. The volume is corrupt
! BD25.part102.rar: CRC failed in \BDMV\STREAM\00005.m2ts. The file is corrupt

I've tried using QuickPAR, but it says the files are not in need of repair. Same with MultiPAR. I could use some help. Thanks.
 

wabid

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Dethryl said:
I'm having an issue that could hopefully be helped. The CRC check fails in SABnzbd and I also get the following errors when using WinRAR.

! BD25.part023.rar: Packed data CRC failed in \BDMV\STREAM\00005.m2ts. The volume is corrupt
! BD25.part102.rar: CRC failed in \BDMV\STREAM\00005.m2ts. The file is corrupt

I've tried using QuickPAR, but it says the files are not in need of repair. Same with MultiPAR. I could use some help. Thanks.

That sounds like there was corruption before the faneditor uploaded the file. I would contact them directly and see if they have a fix.
 

Q2

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wabid said:
That sounds like there was corruption before the faneditor uploaded the file. I would contact them directly and see if they have a fix.

It's already been discussed and resolved. :)
 

NonStopRobotDisco

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Q2 said:
It's already been discussed and resolved. :)

Hi Q2

I'd very grateful if you could also help me with your Fall Of The Jedi - Episode III BD25?

I've successfully been able to download Episodes I and II, without any issue. However, whenever I download Episode III, via NZB or Torrent, there always appears to be a component missing.

In the case of the NZB, I always get the message: "Unpacking failed. these file(s) are missing: Fall of the Jedi - Episode 3/BDMV/STREAM/00005.M2ts". I noticed an Original Trilogy forum, which mentioned that one of the original files may have been corrupt, but have not been able to find an updated version.

I managed to find an 'HD Part 23 Fixed' NZB on usenet, which I had hoped might resolve the issue, but it also appears to have a problem, and I get the following message: "Unpacking failed, unable to find Q2_FOTJ_EP3_1080p_BD25.part024.rar".

I use SABnzbd to download NZB's. Can you advise on what best to do?

Thanks
 

Q2

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It's possible the Usenet files have started to come down since its been 3 years. If you can't get the files to be fixed using the PAR2 then it may not not be salvageable. I no longer offer the BD25 anywhere but I do have a 1080p MKV up if you're interested.
 

NonStopRobotDisco

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Q2 said:
It's possible the Usenet files have started to come down since its been 3 years. If you can't get the files to be fixed using the PAR2 then it may not not be salvageable. I no longer offer the BD25 anywhere but I do have a 1080p MKV up if you're interested.

Hi. Thanks very much for the quick reply. I'll PM you later tonight.
 
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