[pve-devel] [PATCH pve-qemu-kvm] vma: set cache unsafe for performance

[elacunza at binovo.es]

This patch is a follow-up to Alexandre's rbd patch, so that we set cache
unsafe during restore for performance. This is the same done in qemu-img
convert, which defaults to unsafe cache.

In our fixed ceph cluster this has given us a x4 boost (from 15MB/s to 
94MB/s) with a 44% sparse 10GB backup (network is 1gbit, gains could be 
higher)