Why Are My Speeds So Slow?

There are many possible reasons:

1. Is it your network?

If you're not sure whether the problem is a specific torrent or your network, it's easy to get a point of reference -- add a fast torrent for benchmarking. Many users visit ​the Ubuntu torrent page, scan down the page for the line with the most seeders and downloaders, and join the swarm for a few minutes to see what speeds they'll reach.

More generally, you can also measure your bandwidth at ​speedtest.net. However, this is not as good a Bittorrent benchmark as the previous approach.

2. Is your tracker responding?

Trackers are the primary source of finding other peers. When your tracker goes down, finding peers to share with is slower.

Look at the Tracker tab of the torrent dialog and see what it says about the last announce. Did the tracker respond "OK" or was there an error message?

3. Are there too many (or not enough) seeders?

At the bottom of the torrent dialog's Peers tab, you'll see how many seeders and downloaders the tracker says are in the swarm.

If you're seeding and so are most of the other participants, your speeds will be slow because all the seeds are competing for the downloaders' limited bandwidth.

If you're downloading, things are a little better because you can download from everyone else, not just seeds. But if there aren't enough seeds, the swarm will still be congested, and downloaders will all get stuck at the same completeness percentage as they wait for more data to trickle down from the seeds.

4. Is it your speed limits?

This falls into the are-you-sure-it-is-plugged-in category, but don't be embarassed: lots of people have been bitten by this. Note: remember that there are both per-torrent and overall speed limits. :)

5. Is it a small swarm?

Even if you're the only downloader and there are four or five seeds ready to send you information, things can still be slow sometimes. Often what happens is the seeds' upload bandwidth is being shared between you and other peers in another torrent.

6. Is it your ISP?

If your ISP is one of those that manipulates Bittorrent packets -- and even if it isn't -- it's often a good idea to enable the [Blocklist] and also to tell Transmission to "Ignore Unencrypted Peers" to give your sessions slightly better privacy.

Update: Google now has ​a free online tool to test what your ISP is doing. Follow that link and go down to the "Start testing" button.

7. Is it an old version of Transmission?

Many users have reported that 1.50 is much faster than the previous 1.3x and 1.4x releases. If you're using an old version, consider upgrading.

8. Is it your router or firewall making your "port closed"?

Connecting to a peer is like telephone calls: either you call up the peer, or the peer calls you. When Transmission says your "Port is Closed" it's like having a phone that doesn't allow incoming calls: you can still call peers, but they can't call you.

Some people leave their port closed because they reason that dialing out is enough. Other people assume that BitTorrent? won't work with a closed port, and overreact. The truth is in the middle -- you can get by with a closed port, but on average you'll get much faster speeds if peers can connect to you.

For example, peers that join the swarm after you will know about you (because they got your address from the tracker) but you won't know about them. They'll try to connect to you, but if you're not reachable, they'll take their business elsewhere.

Fixing a closed port is possibly the most frustrating task in Bittorrent: It often involves tweaking your firewall, your router, and your router's firewall. The good news is that the Transmission wiki has two pages dedicated to this topic: the Port Forwarding Guide and the Why is my port closed page.

You can also test your port status at ​canyouseeme.org.

9. Is it a Transmission Bug?

If you've looked at all the reasons above and none of them fit -- Ubuntu downloaded quickly, and you've got the latest version of Transmission, and there are plenty of seeds and downloaders in your torrent, yet things are still slow -- then maybe you've found a Transmission bug. Go ​read this post about what information the developers need to diagnose the problem, and then post a message describing your situation.

Make sure to give enough information! Vague bug reports waste everyone's time and will probably just get you referred back to this page. :)