使用block设备来避免额外的software layers。

Best practices: Asynchronous I/O model for KVM guests
尽管KVM supports thread pools for handling asynchronous I/O operations，
can also take advantage of the Kernel Asynchronous I/O (AIO) support for
Linux.
by specifying aio=native in the qemu-kvm command.

Best practice: x2APIC support for Red Hat Enterprise Linux 6 guests.

Best practice: NFS remote storage

Best practice: Device-backed and file-backed virtual storage

Best practice: I/O schedulers

Best practice: Optimize block I/O performance by using the Deadline I/O
scheduler

 Virtio and vhost_net

vhost_net 把部分Virtio驱动从用户态移到kernel

Device Assignment and SR-IOV

6.3. Caching Cache=none

6.4. I/O Mode IO=native

6.5.2. Multi-Queue virtio-scsi