Low speed download if line bandwidth start with 500mb/s-1000mb/s and more, use only TCP

deekerman commented

2026-02-21 20:44:31 -05:00

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Originally created by @1Const1 on GitHub (May 9, 2020).

qBittorrent version and Operating System

Windows 7-10

If on linux, libtorrent-rasterbar and Qt version

none

What is the problem

In qBittorrent 4.2.5 maximum speed on torrents that i can reach is 25-30mb/s. Mostly often only 22-25Mb\s. Then i try anouther client BC 1.66. On BC i can reach 60-65mb/s maximum speed easily on the same torrents. I don't know why qBittorrent works very slow bec. on lines with good speed 500-1000mb/s. Yes, my computer before router, but why outher client BC reach maximum speed of my line and qBittorrent not reached even half speed?

What is the expected behavior

60-65mb/s maximum speed

Steps to reproduce

Download torrents on line bandwidth start with 500mb/s-1000mb/s try reach maximum speed.

Extra info(if any)

I try to switch use only TCP and not use UDP protocol, but it still not let me reach full speed on my internet channel when outer clients can do it. i think it is bug
My HDD is SDD that i use for experiment with speed. SDD can handle much more write speed

Same issue:
https://github.com/qbittorrent/qBittorrent/issues/7888

It's still not fixed.

Originally created by @1Const1 on GitHub (May 9, 2020). ### qBittorrent version and Operating System Windows 7-10 ### If on linux, libtorrent-rasterbar and Qt version none ### What is the problem In qBittorrent 4.2.5 maximum speed on torrents that i can reach is 25-30mb/s. Mostly often only 22-25Mb\s. Then i try anouther client BC 1.66. On BC i can reach 60-65mb/s maximum speed easily on the same torrents. I don't know why qBittorrent works very slow bec. on lines with good speed 500-1000mb/s. Yes, my computer before router, but why outher client BC reach maximum speed of my line and qBittorrent not reached even half speed? ### What is the expected behavior 60-65mb/s maximum speed ### Steps to reproduce Download torrents on line bandwidth start with 500mb/s-1000mb/s try reach maximum speed. ### Extra info(if any) I try to switch use only TCP and not use UDP protocol, but it still not let me reach full speed on my internet channel when outer clients can do it. i think it is bug My HDD is SDD that i use for experiment with speed. SDD can handle much more write speed Same issue: https://github.com/qbittorrent/qBittorrent/issues/7888 It's still not fixed.

deekerman closed this issue

2026-02-21 20:44:33 -05:00

deekerman commented

2026-02-21 20:44:35 -05:00

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@FranciscoPombal commented on GitHub (May 9, 2020):

@1Const1

Same issue:
#7888

If you look in that issue's comments, later on the OP says (https://github.com/qbittorrent/qBittorrent/issues/7888#issuecomment-430606326):

Little update: my win8.1 installation died, i installed 10 instead this time, and with the 4.1.3 on windows 10 there is no more cap on the download, so i'm guessing there was some strange problem with my installation or the app on that OS.

It was due to user error or some problem with their setup, not qBittorrent itself.

With that said, I've always been able to saturate Gigabit connections with qBittorrent, even on very weak machines, as long as the settings are correctly configured and they have an SSD. Same with HDDs, but only if the HDD is not crappy (like a lot of 2.5' HDDs such as the ones in laptops) and if not many downloads are occurring at the same time. libtorrent (qBittorrent's backend) is very efficient. So this is most likely a problem with your setup and/or settings.

First try changing these settings in the advanced settings:

Asynchronous I/O threads to 4 times the number of logical processors in your CPU (so 4*4 = 16 on a 4 core 4 thread CPU, 4*8 = 32 on a 4 core 8 thread or 8 core 8 thread CPU, etc) - see the explanation for this should be this way here under Asynchronous I/O threads.
Disk cache to auto

These changes are aimed at eliminating the chances that:

You are CPU bottlenecked to to qBIttorrent being configured to only hashing on one logical processor
You are I/O bottlenecked due to insufficient disk cache (though since you have an SSD, this is most likely not the case anyway)

If this does not work, please post your entire settings file in plain text (making sure to redact potentially sensitive info) and we'll go from there.

@FranciscoPombal commented on GitHub (May 9, 2020): @1Const1 > Same issue: #7888 If you look in that issue's comments, later on the OP says (https://github.com/qbittorrent/qBittorrent/issues/7888#issuecomment-430606326): > Little update: my win8.1 installation died, i installed 10 instead this time, and with the 4.1.3 on windows 10 there is no more cap on the download, so i'm guessing there was some strange problem with my installation or the app on that OS. It was due to user error or some problem with their setup, not qBittorrent itself. With that said, I've always been able to saturate Gigabit connections with qBittorrent, even on very weak machines, as long as the settings are correctly configured and they have an SSD. Same with HDDs, but only if the HDD is not crappy (like a lot of 2.5' HDDs such as the ones in laptops) and if not many downloads are occurring at the same time. libtorrent (qBittorrent's backend) is very efficient. So this is most likely a problem with your setup and/or settings. First try changing these settings in the advanced settings: - Asynchronous I/O threads to 4 times the number of logical processors in your CPU (so `4*4 = 16` on a 4 core 4 thread CPU, `4*8 = 32` on a 4 core 8 thread or 8 core 8 thread CPU, etc) - see the explanation for this should be this way [here](https://github.com/qbittorrent/qBittorrent/wiki/Explanation-of-Options-in-qBittorrent#libtorrentspecific_configuration) under `Asynchronous I/O threads`. - Disk cache to `auto` These changes are aimed at eliminating the chances that: - You are CPU bottlenecked to to qBIttorrent being configured to only hashing on one logical processor - You are I/O bottlenecked due to insufficient disk cache (though since you have an SSD, this is most likely not the case anyway) If this does not work, please post your entire settings file in plain text (making sure to redact potentially sensitive info) and we'll go from there.

deekerman commented

2026-02-21 20:44:36 -05:00

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@1Const1 commented on GitHub (May 10, 2020):

Asynchronous I/O i made = 32
Disk cache to auto

result the same. 8-30Mb/s. speed always goes down (30-8-14-15-30-20-23-28-9-7-8-16-14-40-17)
expecting 55-65 always

@1Const1 commented on GitHub (May 10, 2020): Asynchronous I/O i made = 32 Disk cache to auto result the same. 8-30Mb/s. speed always goes down (30-8-14-15-30-20-23-28-9-7-8-16-14-40-17) expecting 55-65 always

deekerman commented

2026-02-21 20:44:36 -05:00

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Owner

@FranciscoPombal commented on GitHub (May 10, 2020):

@1Const1

Ok then please:

post your entire settings file in plain text (making sure to redact potentially sensitive info) and we'll go from there.

Also enable both protocols, disabling uTP will just make it so you'll connect to less peers.

@FranciscoPombal commented on GitHub (May 10, 2020): @1Const1 Ok then please: >post your entire settings file in plain text (making sure to redact potentially sensitive info) and we'll go from there. Also enable both protocols, disabling uTP will just make it so you'll connect to less peers.

deekerman commented

2026-02-21 20:44:36 -05:00

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@1Const1 commented on GitHub (May 10, 2020):

Ok got it. i uploaded blow this message qBittorrent.ini from users directory
And enable all protocols nothing changes

qBittorrent.ini.txt

@1Const1 commented on GitHub (May 10, 2020): Ok got it. i uploaded blow this message qBittorrent.ini from users directory And enable all protocols nothing changes [qBittorrent.ini.txt](https://github.com/qbittorrent/qBittorrent/files/4605914/qBittorrent.ini.txt)

deekerman commented

2026-02-21 20:44:36 -05:00

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@FranciscoPombal commented on GitHub (May 10, 2020):

@1Const1 Try disabling your global speed limits as well has your global and per-torrent upload slot limits, as well as keeping the new async I/O threads and disk cache options you set above.

@FranciscoPombal commented on GitHub (May 10, 2020): @1Const1 Try disabling your global speed limits as well has your global and per-torrent upload slot limits, as well as keeping the new async I/O threads and disk cache options you set above.

deekerman commented

2026-02-21 20:44:36 -05:00

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@1Const1 commented on GitHub (May 14, 2020):

Try disabling your global speed limits as well has your global and per-torrent upload slot limits, as well as keeping the new async I/O threads and disk cache options you set above.

I don't have download global limit. Upload limit i canceled without nothing changes for speed limits for described problem

@1Const1 commented on GitHub (May 14, 2020): > Try disabling your global speed limits as well has your global and per-torrent upload slot limits, as well as keeping the new async I/O threads and disk cache options you set above. I don't have download global limit. Upload limit i canceled without nothing changes for speed limits for described problem

deekerman commented

2026-02-21 20:44:36 -05:00

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Owner

@FranciscoPombal commented on GitHub (May 14, 2020):

@1Const1

Upload limit i canceled without nothing changes for speed limits for described problem

Not sure what you mean by this, but due to the nature of Bittorrent (and TCP), you need at least a certain upload speed to reach high download speeds. So try with Upload limits disabled if you haven't yet.

Other than that: try enabling/setting the following advanced settings:

File pool size -> 400
Disk cache expiry -> 60s
Enable OS Cache -> yes
Coalesce reads & writes -> yes

@FranciscoPombal commented on GitHub (May 14, 2020): @1Const1 >Upload limit i canceled without nothing changes for speed limits for described problem Not sure what you mean by this, but due to the nature of Bittorrent (and TCP), you need at least a certain upload speed to reach high download speeds. So try with Upload limits disabled if you haven't yet. Other than that: try enabling/setting the following advanced settings: - File pool size -> 400 - Disk cache expiry -> 60s - Enable OS Cache -> yes - Coalesce reads & writes -> yes

deekerman commented

2026-02-21 20:44:36 -05:00

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@1Const1 commented on GitHub (May 19, 2020):

File pool size -> 400

Disk cache expiry -> 60s

this two i think was helpful. now speed increasing to better results like 44-48 mb/s. it's looks much more good than was before. if it's possible need use this settings by default and update installers qBitTorrent

Enable OS Cache -> yes
Coalesce reads & writes -> yes

this two was as described already, so i did't change them

FranciscoPombal, thank you for help

@1Const1 commented on GitHub (May 19, 2020): > * File pool size -> 400 > * Disk cache expiry -> 60s this two i think was helpful. now speed increasing to better results like 44-48 mb/s. it's looks much more good than was before. if it's possible need use this settings by default and update installers qBitTorrent > Enable OS Cache -> yes > Coalesce reads & writes -> yes this two was as described already, so i did't change them **FranciscoPombal,** thank you for help

deekerman commented

2026-02-21 20:44:36 -05:00

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@FranciscoPombal commented on GitHub (May 20, 2020):

@1Const1

File pool size -> 400

Disk cache expiry -> 60s

this two i think was helpful. now speed increasing to better results like 44-48 mb/s. it's looks much more good than was before. if it's possible need use this settings by default and update installers

Disk cache expiry -> 60s

This is the default, so unless you had it previously set to another value, I don't think this affected the result at all.

Now, for the other setting,

File pool size -> 400

the default is 40. You could try increasing it to something like 2000 or 4000. Do the torrents that you're testing with happen to have a lot of files?
You can also try disabling anti-virus and see the difference that it makes.

More info: https://libtorrent.org/single-page-ref.html#file_pool_size

@FranciscoPombal commented on GitHub (May 20, 2020): @1Const1 > > * File pool size -> 400 > > * Disk cache expiry -> 60s > > this two i think was helpful. now speed increasing to better results like 44-48 mb/s. it's looks much more good than was before. if it's possible need use this settings by default and update installers > * Disk cache expiry -> 60s This is the default, so unless you had it previously set to another value, I don't think this affected the result at all. Now, for the other setting, > > * File pool size -> 400 the default is 40. You could try increasing it to something like 2000 or 4000. Do the torrents that you're testing with happen to have a lot of files? You can also try disabling anti-virus and see the difference that it makes. More info: https://libtorrent.org/single-page-ref.html#file_pool_size

deekerman commented

2026-02-21 20:44:36 -05:00

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@1Const1 commented on GitHub (May 21, 2020):

This is the default, so unless you had it previously set to another value, I don't think this affected the result at all.

Yes it was 60, you are right. i checked on outer installation
I din't change advanced settings before receiving recommendations from this topic

the default is 40. You could try increasing it to something like 2000 or 4000. Do the torrents that you're testing with happen to have a lot of files?
You can also try disabling anti-virus and see the difference that it makes.

Ok, i will try later. i have around 400 torrents active-finished on upload mode, sometimes 10 active in same time, but in other time only one torrent active download (only 1-2 file in it) and with param File pool size =40 speed was very slow as i described

i hope increasing this parameter does not killing disk (ssd or regular hdd)?

antivirus - i use only that included in OS by default defender - that's all

@1Const1 commented on GitHub (May 21, 2020): > This is the default, so unless you had it previously set to another value, I don't think this affected the result at all. Yes it was 60, you are right. i checked on outer installation I din't change advanced settings before receiving recommendations from this topic > the default is 40. You could try increasing it to something like 2000 or 4000. Do the torrents that you're testing with happen to have a lot of files? > You can also try disabling anti-virus and see the difference that it makes. Ok, i will try later. i have around 400 torrents active-finished on upload mode, sometimes 10 active in same time, but in other time only one torrent active download (only 1-2 file in it) and with param File pool size =40 speed was very slow as i described i hope increasing this parameter does not killing disk (ssd or regular hdd)? antivirus - i use only that included in OS by default defender - that's all

deekerman commented

2026-02-21 20:44:36 -05:00

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Owner

@FranciscoPombal commented on GitHub (May 21, 2020):

@1Const1

Ok, i will try later. i have around 400 torrents active-finished on upload mode, sometimes 10 active in same time, but in other time only one torrent active download (only 1-2 file in it) and with param File pool size =40 speed was very slow as i described

The number of torrents doesn't really matter, it's the number of actual files that matter.

i hope increasing this parameter does not killing disk (ssd or regular hdd)?

No. This only concerns file descriptors, which handles at the OS level used to to keep track of open files in memory. On Linux, for example you can tune the limit of open file descriptors per process.

antivirus - i use only that included in OS by default defender - that's all

Anti-virus (does not matter which) have the bad habit of interfering with everything other applications do, including opening/closing file descriptors, and using a lot of disk I/O. I recommend testing at least once with anti-virus disabled (via group policy, see https://www.windowscentral.com/how-permanently-disable-windows-defender-antivirus-windows-10#disable_defender_grouppolicy), just to compare speeds.

P.S. - If you know what you are doing, you don't need an anti-virus, they are basically a scam (although other Windows users will claim this is heresy, but they don't understand how computers work). Just use a firewall, FOSS software and an adblocker for the web (like ublock origin) and install security updates for your OS and programs regularly and you'll be fine. If you follow these recommendations, there's nothing extra an anti-virus will do for you. On the other hand, if you have a habit of executing random exes you find online, sometimes not even an anti-virus will be able to help you...

@FranciscoPombal commented on GitHub (May 21, 2020): @1Const1 > Ok, i will try later. i have around 400 torrents active-finished on upload mode, sometimes 10 active in same time, but in other time only one torrent active download (only 1-2 file in it) and with param File pool size =40 speed was very slow as i described The number of torrents doesn't really matter, it's the number of actual files that matter. > i hope increasing this parameter does not killing disk (ssd or regular hdd)? No. This only concerns _file descriptors_, which handles at the OS level used to to keep track of open files in memory. On Linux, for example you can tune the limit of open file descriptors per process. > antivirus - i use only that included in OS by default defender - that's all Anti-virus (does not matter which) have the bad habit of interfering with everything other applications do, including opening/closing file descriptors, and using a lot of disk I/O. I recommend testing at least once with anti-virus disabled (via group policy, see https://www.windowscentral.com/how-permanently-disable-windows-defender-antivirus-windows-10#disable_defender_grouppolicy), just to compare speeds. P.S. - If you know what you are doing, you don't need an anti-virus, they are basically a scam (although other Windows users will claim this is heresy, but they don't understand how computers work). Just use a firewall, FOSS software and an adblocker for the web (like ublock origin) and install security updates for your OS and programs regularly and you'll be fine. If you follow these recommendations, there's nothing extra an anti-virus will do for you. On the other hand, if you have a habit of executing random exes you find online, sometimes not even an anti-virus will be able to help you...

deekerman commented

2026-02-21 20:44:36 -05:00

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@xavier2k6 commented on GitHub (Dec 17, 2023):

qBittorrent 4.2.5

Version is obsolete.

Thank you for your contribution, we are starting to close all old/stale/obsolete tickets.

Please update to latest qBittorrent 4.6.2 ATTOW.

If any issues are experienced, please open a new ticket.

Windows Users: (Note: Windows 10 1809+ / Windows Server 2019 required as minimum)

@xavier2k6 commented on GitHub (Dec 17, 2023): >qBittorrent 4.2.5 Version is obsolete. Thank you for your contribution, we are starting to close all old/stale/obsolete tickets. Please update to latest qBittorrent 4.6.2 ATTOW. If any issues are experienced, please open a new ticket. Windows Users: (Note: Windows 10 1809+ / Windows Server 2019 required as minimum)

Rows
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Low speed download if line bandwidth start with 500mb/s-1000mb/s and more, use only TCP #10406

qBittorrent version and Operating System

If on linux, libtorrent-rasterbar and Qt version

What is the problem

What is the expected behavior

Steps to reproduce

Extra info(if any)