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Multi file torrents and cross-file pieces


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I just recently started using torrents and have a question about cross-file pieces in multi file torrents.

I am downloading a torrent that has about 100 files in it and I don't wan't all the files. I downloaded two files next to eachother and then deleted one of them. Forced a recheck and the file I kept was around 99% now instead of 100.

I did some searching and found that this was b/c of cross-file pieces being deleted. I downloaded the pieces again and I was wondering, when i'm done seeding and decide to move the file to a different location, such as an external drive, is it going to take all the cross file pieces that it needs from the files I didn't download with it and rebuild the individual files correctly?

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You'll still have the full files if you copy/move them around, but when you try to upload them again they'll show as missing their edge pieces because those edge pieces overlap with other files. It may be possible to move uTorrent's partial files with the completed files and get uTorrent to see whole edge pieces...but I've never used that. :P

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I'm still not 100% sure how it works. How would it work with these two situations.

Say I have 3 files (A,B, and C). They overlap as shown below.


1. I only wan't file B and I tell it to skip A an C.

It then downloads file B including the cross-file pieces around it in A and C.

How is it saved to my hard drive right now with the torrent file still loaded in uTtorrent. Is there one complete file or is it saved in three different files?

2. I download all the files (A, B, and C).

I then decide I don't wan't to keep A and C.

I go to the hard drive folder and delete A and C.

Now, did I just delete the beginning and end of file B?

I know from this point uTorrent will not be able to seed any longer b/c it thinks it lost the cross-file pieces of file B, but do I still have the entire file B on my hard drive?

After deleting A and C, can I just move file B from my hard drive to another location and have the whole file or do I have to recheck the file in uTorrent and let it redownload the cross-file pieced before I move it?

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I think I figured it out. I have a file named "~uTorrentPartFile_9E8F4CE71". It is 16.9 MB. I would assume that is a file filled with the partial files and the partial files are also saved with the main files on my hard drive to make them complete. So, theres really duplicates of the partial files on my hard drive for the purpose of seeding and they get removed when the torrent is removed.

2. You just deleted the beginning and end pieces of B.

But you DO still have the entire file B on your hard drive.

Just to claify, your saying that I am deleting the part files from the uTorrent partfile file and will not be able to seed, but I still do have those files with the main file on my hard drive.

So with both situations, if I only download B or download A, B, and C and then delete A and C, I will still have the entire file B 100% in the location I saved it to.

It's confusing b/c when I rechecked the file it said I only had 99% and I thought it was actually missing part of the file.

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Thanks for your help. I understand now.

I don't know anything about programming, but would it be that hard when you recheck a torrent to have uTorrent scan all the files that are associated with that torrent and realise that the partial pieces are there and then just copy those pieces to the partfile file? That would be much easier that redownloading the pieces.

It sounds simple in theory, but i'm guessing its not that easy since it hasn't been done yet.

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I'll try it some time with a smaller file. I'm busy now and don't want to mess with whats downloading since I have a slow 1 megabit DSL connection.

I think I remember reading somewhere that someone tried moving the partfile and then they couldn't get uTorrent to recognise it again.

Maybe i'll try something like:

Download A, B, and C

Copy the full partfile like a backup. That way it has all the parts of B.

Delete A and C only keeping B.

Use the backup copy of the original partfile and put it in place of the new smaller partfile that is missing parts of B.

Then recheck and see if it's all there.

Edit: I have another torrent that only has three files. Over 14 MB of partfiles. I made a copy of the partfiles to the desktop and then deleted the original partfiles. Rechecked and the 3 files went down to 96.6, 98.1, and 97.9%.

I then deleted the new partfile file it made (which had almost nothing in it) and put the old one back in. Rechecked again and all three were at 100% again.

So, you can copy the partfile and replace it, but I didn't try deleting a file yet. I'll try that tomorrow or sunday.

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  • 3 years later...

Sorry for bringing up an old thread but I am still a bit unclear on this.

Using the examples already given, I have a torrent with files A B C and only download B (while skipping A and C). When B is 100% complete, am I able to transfer it to an external hard drive by itself or am I missing parts of B? I don't care about seeding or having uTorrent recognize it as being 100%, I just want to be able to transfer B as a full, uncorrupted file to an external drive.

I am pretty sure I know the answer, but I just want to be positive.

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  • 1 year later...


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