[fedora-virt] qcow2 and virtio in virt-preview and rawhide

[Gianluca Cecchi]

Hello,
testing in F14 + virt-preview repo with qemu 0.13.91
Installing a CentOS 5.5 guest with virtio disk in qcow2 format on a
directory based storage pool seems quite slow (default text install
for 2,5Gb of data takes about 33 minutes)

Changing cache mode to writeback improves very much.
What is the risk of writeback and what is the default?
What would be advisable as a good compromise between speed and data
safeness in this version of qemu?

Thanks,
Gianluca