For virtual disks you can specify cache and io to use, it would be great if: a) New guests got the defaults filled in there so people could see that they could adjust them. b) virt-install could see if the storage pool was lvm say and set it to cache=none, io=native or if it was a qcow2/raw file it could be cache=writeback or the best options there.
This bug appears to have been reported against 'rawhide' during the Fedora 20 development cycle. Changing version to '20'. More information and reason for this action is here: https://fedoraproject.org/wiki/BugZappers/HouseKeeping/Fedora20
Upstream sets cache=none and io=native for block devices now. One problem with encoding the the current writeback default in the XML is that if qemu ever changes its defaults, we are stuck with the old one. Would be nice if libvirt hade a cache=hvdefault setting or similar here but they tend to avoid those things.
virt-manager-0.10.0-4.git79196cdf.fc20 has been submitted as an update for Fedora 20. https://admin.fedoraproject.org/updates/virt-manager-0.10.0-4.git79196cdf.fc20
Package virt-manager-0.10.0-4.git79196cdf.fc20: * should fix your issue, * was pushed to the Fedora 20 testing repository, * should be available at your local mirror within two days. Update it with: # su -c 'yum update --enablerepo=updates-testing virt-manager-0.10.0-4.git79196cdf.fc20' as soon as you are able to. Please go to the following url: https://admin.fedoraproject.org/updates/FEDORA-2013-18473/virt-manager-0.10.0-4.git79196cdf.fc20 then log in and leave karma (feedback).
virt-manager-0.10.0-4.git79196cdf.fc20 has been pushed to the Fedora 20 stable repository. If problems still persist, please make note of it in this bug report.