Large file processing outside of home directory problems

[shag00]

Operating System: Kubuntu 20.10
KDE Plasma Version: 5.19.5
KDE Frameworks Version: 5.74.0
Qt Version: 5.14.2
Kernel Version: 5.8.0-21-generic
OS Type: 64-bit
Processors: 16 × AMD Ryzen 7 3700X 8-Core Processor
Memory: 15.6 GiB of RAM
Graphics Processor: GeForce GTX 1080/PCIe/SSE2

Processing large files (50GB+) is a problem when they are resident outside of the home directory, in my case on a second HDD. The problem occurs with a number of programs such as Tixati, MKVtoolnix, VLC and MPV. The problems caused start at very high CPU usage and slow system responce through to freezing of an application where mouse movement is not possible/visible though it is visible and moveable outside of the affected window. I first noticed the problem on 20.04 and it is still present under 20.10. I am using Kubuntu and initially raised a KDE bug which was closed and reported as fixed upstream but it appears not to have been. (https://bugs.kde.org/show_bug.cgi?id=426580)

My system has a number of drives, M2, SSD and mechanical HDD, the home directory is on a M2 NVME drive. Transfer speeds between the M2 drives is typically 1.1GB/s and between the mechanical HDD 160-170 MB/s, indicating they are working correctly and are in any case very new. Gsmartcontrol does not indicate any issue with the drives.

As an example I ran MKVtoolnix a number of times, processing the same file, on a few different disks and came up with wildly diverging processing times:

M2 home directory 4 minutes 25 seconds
2nd M2 drive 16 minutes 0 seconds
1st and 2nd mechanical HDD both around 170 minutes

As it is a dual boot machine I performed the same test on Windows using one of the mechanical HDD and it took 16 minutes 4 seconds.

The test consisted of remuxing and m2ts file to a mkv file, the input size was 58GB and the output size was 52 GB. I used MKVtoolnix version 51 and each file was read and written to the same disk.

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: ubuntu-release-upgrader-core 1:20.10.12
ProcVersionSignature: Ubuntu 5.8.0-21.22-generic 5.8.13
Uname: Linux 5.8.0-21-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu49
Architecture: amd64
CasperMD5CheckResult: skip
CrashDB: ubuntu
CurrentDesktop: KDE
Date: Sun Oct 11 16:40:59 2020
InstallationDate: Installed on 2020-01-06 (279 days ago)
InstallationMedia: Kubuntu 19.10 "Eoan Ermine" - Release amd64 (20191017)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
Symptom: ubuntu-release-upgrader
UpgradeStatus: Upgraded to groovy on 2020-10-10 (0 days ago)
VarLogDistupgradeXorgFixuplog:
 INFO:root:/usr/bin/do-release-upgrade running
 INFO:root:No xorg.conf, exiting