[ovirt-users] Windows 2012R2 virtio-scsi abysmal disk write performance

[Jean-Francois Courteau]

Hello there,

I just installed oVirt on brend new machines. The engine on a Virtualbox
VM in my current infrastructure, and a single dedicated CentOS host
attached to the engine.

I am getting extremely poor write performance in my oVirt Windows 2012R2 
VM, whatever the virtio, virtio-scsi device I use, and whatever the 
virtio Windows driver version.

Here are my host specs (srvhc02):

CPU: Intel(R) Core(TM) i7-4790 CPU @ 3.60GHz (4C 8T)
Mem: 32GB DDR3
Disks:
   - 2 x WD Black 2TB (RAID1) where the CentOS is installed
   - 4 x WD Gold 4TB (RAID10) dedicated for a storage domain (/dev/md0,
ext4, mounted in /storage and exported with NFS with default settings)
NIC: Intel 4 ports Gigabit. One port for VMs, one port for everything
else. 2 unused ports.
OS: Freshly installed CentOS 7 minimal latest (yum updated)
oVirt deployed from the Engine using root account with a password

Here are my Engine specs (srvvmmgmt):

Virtualbox guest VM in another physical computer just for test purposes.
CPU: 2vCPU
Mem: 8GB
Disk: 50GB VDI on a RAID10 array
NIC: Virtual Intel Pro 1000 (Bridged over a physical Intel 4 ports
Gigabit)
OS: Freshly installed CentOS 7 minimal latest (yum updated)
oVirt Engine 4.2 deployed from the repo, yum updated yesterday
Storage domain: NFS - srvhc02:/storage
ISO domain: NFS - srvhc02:/iso

Physical network is Gigabit on Cisco switches, no VLAN tagging.

My (barely usable) Windows 2012R2 guest (srvweb03)
CPU: 2vCPU
Mem: 8GB
Disk1: 100GB on the storage domain
Disk 2: 200GB on the storage domain (this is the one I was changing the
controller for testing purposes)
NIC: virtio bridged over the VM port

I have tried every possible combination of drive controller
(virtio-scsi, virtio, IDE), virtio drivers (stable and latest from the
Fedora website, others found in sometimes obsucre places), and the disk
write performances are simply unacceptable. Of course I had a reboot
between each NIC driver update and driver change.

I have compared with a Virtualbox installed on the same host after I
cleaned up oVirt, and the host is absolutely not problematic. Here is
the compare:

                        oVirt            Virtualbox
-----------------------------------------------
SEQUENTIAL READ      *3000MB/s          406MB/s
SEQUENTIAL WRITE      31MB/s            164MB/s
4k RANDOM READ       *400MB/s           7.18MB/s
4k RANDOM WRITE       0.3MB/s(80IOPS)   3MB/s (747IOPS)

*this is ridiculously high, oVirt probably reading from RAM

These performances are using the virtio-scsi in oVirt (any version, none
gave me better performance), and the SATA driver in Virtualbox. Needless
to say that this is frustrating.

I have tried with oVirt virtio-blk (virtio in the interface) driver, it
gave me a 10-15% improvement, but never up to the level I could expect
from an enterprise grade solution. I also tried IDE. I could not even
write at 10kbps on it. I had approx 10IOPM (yes, IO per minute!) with
it.

Is there something I am missing?

Thanks!