Alright, I have run some more tests:

I copy a file in my (unencrypted, ext4, on root partition) homedir with:

dd if=testfile_8gb of=testfile_out status=progress

(I made the testfile using dd if=/dev/zero of=testfile_8gb bs=1M
count=8000 status=progress)

While running this Xorg/Gnome3/Mouse/Any UI application becomes
unresponsive for seconds at a time, with intervals of a few seconds
where everything is responsive. The write speed of dd often starts
somewhere between 200 and 100 mb/s and then dips all the way to around
35, after which the dd process completely locks up. (I think this is
because the process gets stuck into some kind of iowait state, I deduced
this from some quick peeks at KSysGuard, citation needed). After a few
minutes the dd process suddenly finishes and the UI becomes responsive
again. Copying the file through nautilus has similar behaviour.

Disabling intel_pstate via the kernel boot parameters
(intel_pstate=disabled) did not have any effect (except for indeed
disabling intel_pstate).

Doing some tweaks to the vm dirty bytes settings had no significant
effect (making the mouselag more of a jitter, but still unusable).

Disabling the swapfile (19.10 has a swapfile instead of swap partition
by default) however completely mitigated the issue!

If some people are willing to try to reproduce this we might be able to
get something going:

- Open some Youtube video in Firefox (something that lets you see if the UI 
lags)
- next to that open two terminals, in one terminal start the dd process as 
described above
- The ui should be lagging now, mouse doesn't move for seconds at a time, 
youtube video severaly lags/hangs/jitters
- in the second unused terminal run 'sudo swapoff /swapfile'
- For me the lag immediately stops
- Killing the dd process/letting it finish and then starting a new one works 
perfectly, much higher writespeeds (and more stable)
- enable swag again with 'sudo swapon /swapfile'
- Lag returns completely

I am really curious if this works for others. Maybe this is an entirely
different issue, for which I will file a bugreport if nobody can
reproduce this.

Thanks in advance!

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You received this bug notification because you are a member of Kernel
Packages, which is subscribed to linux in Ubuntu.
https://bugs.launchpad.net/bugs/1208993

Title:
  Ubuntu slows down and hangs while copying file from/to USB

Status in linux package in Ubuntu:
  Confirmed

Bug description:
  Hi

  While copying many and large files to and from a USB drive, the system
  becomes incredibly slow and sometimes hangs. I watched the system
  monitor while it was running slowly but cpu was not above 50% at any
  time, the same for memory.

  I'm using the "WD my passport" HD with a USB3 port of my "ASUS K55VD"
  laptop.

  Description:  Ubuntu 13.04
  Release:      13.04

  nautilus:
    Installed: 1:3.6.3-0ubuntu16
    Candidate: 1:3.6.3-0ubuntu16
    Version table:
   *** 1:3.6.3-0ubuntu16 0
          500 http://ubuntu-archive.mirror.nucleus.be/ raring/main amd64 
Packages
          100 /var/lib/dpkg/status

  
  Steps to reproduce:
  1) Aquire many large files (like your totally legit moviecollection)
  2) Copy files to external HD
  3) Open your browser and be sad when your system becomes incredibly slow 
after a few minutes


  This is my first bugreport so if I'm missing something, please tell
  me.

  ProblemType: Bug
  DistroRelease: Ubuntu 13.04
  Package: nautilus 1:3.6.3-0ubuntu16
  ProcVersionSignature: Ubuntu 3.8.0-27.40-generic 3.8.13.4
  Uname: Linux 3.8.0-27-generic x86_64
  ApportVersion: 2.9.2-0ubuntu8.1
  Architecture: amd64
  Date: Tue Aug  6 22:56:34 2013
  EcryptfsInUse: Yes
  ExecutablePath: /usr/bin/nautilus
  GsettingsChanges:
   b'org.gnome.nautilus.window-state' b'geometry' b"'656x715+154+151'"
   b'org.gnome.nautilus.window-state' b'maximized' b'true'
  InstallationDate: Installed on 2013-05-31 (67 days ago)
  InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
  MarkForUpload: True
  SourcePackage: nautilus
  UpgradeStatus: No upgrade log present (probably fresh install)

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