﻿id,summary,reporter,owner,description,type,status,component,version,resolution,keywords,cc,guest,host
17573,"Regression: ""Use Host I/O cache"" setting seems to be inverted in 5.2 => fixed in SVN/next maintenance",Michi,,"I believe that between 5.1 and 5.2 some change led to an inversion of the ""Use Host I/O cache"" setting.

I mark this bug as critical as people that explicitly disable Host I/O caching to ensure data integrity in case of a power outage may now actually have Host I/O caching enabled and are in danger of loosing data in power outage/reset situations.


Using VirtualBox for testing system installations I activate the Host I/O caching setting to increase performance when installing a lot of RPMs in the virtual machine, particularly because the VDI file on the host resides on a mechanical HDD. When switching from VirtualBox 5.1 to 5.2, I noticed a considerable slowdown.

I measured the slowdown with an ansible playlist that brings a minimal system (installed with Fedora kickstart) to a production level system. The script spends most time on installing RPMs.

Some stats of the RPM installation:
Number of RPM packages before: 324
Number of RPM packages after: 1490
Total file size of all RPMs before: 734 MiB
Total file size of all RPMs after:  3.9 GiB

It is Fedora (guest) on Fedora (host).

This is with the old VirtualBox 5.1, where everything worked as expected.
Installation run on VirtualBox 5.1.32, ""Use Host I/O cache"" activated:

real    7m38.936s
user    0m19.646s
sys     0m3.937s


Going to VirtualBox 5.2 the effect of the setting seems inverted:
Installation run on VirtualBox 5.2.6, ""Use Host I/O cache"" activated:

real    52m17.548s
user    1m22.884s
sys     0m17.828s


Installation run on VirtualBox 5.2.6, ""Use Host I/O cache"" deactivated:

real    10m3.771s
user    0m22.089s
sys     0m5.119s


And here I confirm that the test version is still affected:
Installation run on VirtualBox 5.2.7, ""Use Host I/O cache"" activated:

real    37m57.730s
user    1m13.114s
sys     0m15.521s


Installation run on VirtualBox 5.2.7, ""Use Host I/O cache"" deactivated:

real    11m1.805s
user    0m29.377s
sys     0m5.790s


",defect,closed,virtual disk,VirtualBox 5.2.6,fixed,,,Linux,Linux
