Causes for perpetual hash fails?

So, I am curious for a technical view of what the different causes for a seeder sending not a single healthy piece of a file they are seeding would be. Many different pieces, all failing hash check, without exception. My client bans them, then they come back after the ban expires, feed me 5 or so more pieces that all fail the hash check, then get banned again. I have never seen this before in my peer lists, so I have to ask what the possible causes are, and what the probable causes are. The peer is in the same country as me and is confounding me on several files that they are only seeder on.

Happened to me once before. I'd get about 80% of a piece before the check fails and it's reset. Reported it to a staffer and they said nothing could be done about the fact that a torrent I was downloading which was 4gb large had downloaded 20+gb's (ratio woes, oh how you treat me).

Happens most often on MP3 files. A user changes the tags on the files and saves them, while they are still seeding in their client. Their bittorrent client has no reason to suspect the files have changed. so it keeps sending pieces, unaware that they do not hash properly.

There are many reasons why peers send bad data. It simply means that the data was not saved correctly or has been modified in some way.
Mostly it's a faulty HD but it could be anything on the remote machine that changes the original files.
A good client can detect those peers and ban them. I can even set specific rules when to ban peers.

http://img248.imageshack.us/img248/5...o20110215u.png

I can also choose if the ban is permanent or lifted after a certain period.

When your client doesn't support this, it may happen that you download gigs of bad data that are all counted towards your download stats. Happened to me on HDBits some years ago.

Now if there's only one seeder with corrupt data there's nothing you can do but ask for another seeder that has the proper files. Never happened to me to be honest.

It's also true that you'll find more bad peers on music trackers because people manually change the files they're still seeding.

I advice everyone to use a client that detects and bans these peers. Otherwise there may be some ratio suprises.

:fst:

I actually learnt something new and useful today. Thank you, cbb/Polarbear. I could never explain why this happened before or what would cause it, but now I know the why and how, thanks to you two.

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Originally Posted by Darth Rings

:fst:

I actually learnt something new and useful today. Thank you, cbb/Polarbear. I could never explain why this happened before or what would cause it, but now I know the why and how, thanks to you two.

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I second that, and chrisbeebops post specifically, as I am sure that is exactly what is wrong. I have never been a big audiophile, so I am not terribly in tune with mp3 tracks, but seeing as these are all audio, it fits the scenario perfectly. :)

Besides what the guys above said (which is a pretty thorough explanation), it could also happen that the problem is in your side. This is less likely, but if you have a faulty RAM stick or hard drive or even a malfunctioning router you can also get hashfails, and I've seen it happen.

uTorrent also has settings like the ones Polarbear posted a screen of, although less intuitive - they're found under "Advanced Settings", but that's nothing a quick look at the help file can't help you with.

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Originally Posted by anon-sbi

Besides what the guys above said (which is a pretty thorough explanation), it could also happen that the problem is in your side. This is less likely, but if you have a faulty RAM stick or hard drive or even a malfunctioning router you can also get hashfails, and I've seen it happen.

uTorrent also has settings like the ones Polarbear posted a screen of, although less intuitive - they're found under "Advanced Settings", but that's nothing a quick look at the help file can't help you with.

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Yeah, I already had it set to ban, but not for long enough, and wouldn't have been bothered if they weren't the only seeder. I know it's not on my end, as all the failed pieces were from the same peer, and due to ipv6, they were connecting and getting banned multiple times, on multiple torrents, so I know the prob was on their end. Log files ftw.(sort of) I was more curious about the why, and would rather ask than assume to know ;) I can now guess that it's either someone who routinely renames files, or someone with a dying drive, though the renaming seems much more likely in this instance.

You can rename files and seed them, that's fine. With Azureus you can even move them to different folders. Tagging is what changes them. All you need to do is open a mp3 you're still seeding with iTunes. With the wrong settings it'll change the tags.

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Originally Posted by Polarbear

You can rename files and seed them, that's fine. With Azureus you can even move them to different folders. Tagging is what changes them. All you need to do is open a mp3 you're still seeding with iTunes. With the wrong settings it'll change the tags.

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Hmm... Interesting. Thanks for the clarification, I don't use itunes, so I don't have much exposure to those types of issues.

The same holds true for other media players, especially if they keep track of playcount (it's often added as a tag).

I think Mediamonkey keeps tags in an external DB (or can be set to). There used to be a foobar plugin for that but it's buggy and only works on the older 0.8.x versions. I wish they had something similar for the 1.x series :(

So, I am getting the impression that this could become a more pronounced problem as external devices become more common as the primary source of audio consumption? I am actually getting more stumped by this as I learn more. I would think that it would be a much more common problem if most media players retag any files played through them, or I just misunderstand the way those media player interfaces are set by default. Do you have to opt for the changing of tags consciously, or is it default action? 99% of my media consumption is with VLC, and it is minimal by default.

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Originally Posted by Intr4ns1t

I know it's not on my end

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I only said it can be, sometimes. The vast majority of the time the other guy is to blame. :D

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Originally Posted by Intr4ns1t

99% of my media consumption is with VLC, and it is minimal by default.

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I use Winamp, and never ever had these issues. Some iTunes users keep a copy of their music albums for use with that program just to avoid this. :ermm:

In iTunes all you need to do is disable "sound check". I'm not sure if it's enabled by default. I hardly use iTunes for playback because it doesn't support FLAC. I mostly use Vox and XBMC. These as well as VLC don't change tags by default.

Don't know about the countless other players.

^Not true, it still adds a playcount tag. Disabling Soundcheck just removes Apple's lulzworthy proprietary attempt at ReplayGain.

Personally I just leave a second copy seeding if it's badly tagged, or just stop seeding it period. Foobar stores playcount in its internal settings, so as long as there aren't real issues with the tags it works fine. It'd still be nice to have a completely external tag database again though.

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Originally Posted by ca_aok

^Not true, it still adds a playcount tag.

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No.

If so, that's a recent development.

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Originally Posted by Polarbear

With Azureus you can even move them to different folders.

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You can do that very easily with uTorrent as well.

Some sites actually track how much bad data you upload...
I know oink used to even back in the day.
I do on my site as well though I don't remove data amounts from your downloaded data.
(Oink used to remove it from your downloaded totals if I recall correctly.)
Its just something I started tinkering with a few months ago just to see how many users were receiving bad data.
This is actually the first time I mentioned that I do this anywhere btw. Curious to see if anyone else checks bad data.