My KVM guest does max. 200MB/s although the host does easily > 700MB/s (Raid 0 with 4 SSDs).
Configuration: File-based storage (raw), cache none.
Host 24 cores, 96GB ram, Ubuntu 12.04.1 LTS and virt-manager.
I suspect the CPU to be the bottleneck (one core goes up during hdparm).
Anyone experienced the same or has an explanation ?
Edit: one more info: guest is the same as host (Ubuntu 12). Same poor disk performance observed with Windows 2008 R2 and Suse Enterprise Linux (9 or 10 I think). Max 1 guest running.