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Whenever I run any torrent program on my Ubuntu 12.10, after a short time the download speed drops to zero and all connections (including HTTP connection my browser establishes) start dropping like flies, and pinging any server (like results in 9+ second delays. When I close the torrent program, everything goes back to normal.

It's not a hardware problem, it doesn't occur when I boot from Ubuntu installation flash stick. What could be causing this issue?

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This sounds like your modem/router cannot keep up with the number of connections you are trying to make. – Ramhound Mar 5 '13 at 12:03
@Ramhound, I repeat, this problem doesn't occur when running from fresh distro. – Alexei Averchenko Mar 5 '13 at 12:06
When this behavior happens if you close all your torrent connections does your internet return to normal? Your original statement didn't make a great deal of sense, don't act like, a simple missing word makes all the difference. – Ramhound Mar 5 '13 at 12:13
@Ramhound "if you close all your torrent connections does your internet return to normal?" Yes. – Alexei Averchenko Mar 5 '13 at 12:16
So torrenting from the LiveCD doesn't cause this, but from your normal Ubuntu install does? Are you sure the settings in both cases are exactly the same? The torrent app on the LiveCD might have conservative default settings in place for number of connections, DHT disabled etc. – Karan Mar 6 '13 at 3:54
up vote 1 down vote accepted

Your attempted writes to disk are probably the culprit.

When you boot from the USB stick, your OS/apps (such as BT) are running from there presumably, while your torrent data is recorded to your internal HD (I'm guessing, again).

In your normal setup, you're using a single disk (your internal HD) for A. your currently running OS B. your currently running programs (BT and browser at least, per your example) C. writing the actual torrent data to (extremely demanding with all the seeks, and BT's 'blocks' structure and such)

Well, you're asking for trouble. You're likely also going into swap, compounding the problem further. I realize dropped connections and disk writes are not the same animal, but going into swap can make funny things happen where queueing of tasks and responsiveness is concerned.

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It didn't use to happen (even with the same hardware), so unless fragmentation can cause this, I dunno... – Alexei Averchenko Mar 6 '13 at 6:07

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