[ovirt-users] Poor guest write speeds

[Alan Murrell]

Hello,

I am running oVirt 3.5 on a single server (hosted engine).  I have two
Western Digital WD20EZRX drives in a hardware RAID1 configuration.  My
storage is actually on the single server, but I am attaching to it via NFS.

I created a Windows 7 guest, and I am finding its write speeds to be
horrible.  It is a VirtIO-SCSI drive and the guest additions are installed.

The installation of the OS took way longer than bare metal or even
VMware.  When I ran Windows updates, it again took a *lot* longer than
on bar metal or on VMware.

The read speeds seem to be fine.  The guest is responsive when I click
on programs and they open about as fast as bare metal or VMware.

I downloaded and ran "Parkdale" HDD tester and ran a test with the
following settings:

  - File size: 4000
  - Block Size: 1 MByte

The results are as follows:

  - Seq. Write Speed: 10.7 MByte/sec  (Random Q32D: )
  - Seq. Read Speed: 237.3 MByte/sec  (Random Q32D: )

I ran another test, but this time changing the "Block Size" to "64 kByte
[Windows Default]".  Results are as follows:

  - Seq. Write Speed: 10.7 MByte/sec  (Random Q32D: )
  - Seq. Read Speed: 237.3 MByte/sec  (Random Q32D: )

On the host, running '|dd bs=1M count=256 if=/dev/zero of=test
conv=fdatasync|' on my data mount via NFS rsuled in the following:

256+0 records in
256+0 records out
268435456 bytes (268 MB) copied, 3.59431 s, 74.7 MB/s

I got this <https://romanrm.net/dd-benchmark> and measures the write
speed of a disk.  As you can see, it is significantly higher than what I
am getting in the Windows guest VM.

Running that same "dd" test on an Ubuntu guest VM gives me 24MB/s.

Any ideas why I have such poor write performance?  Is this normal with
oVirt guests?  Any ideas on what I might be able to do to improve them? 
I don't expect to get close to the "bare metal" results, but maybe
something in the 40-60 MB/s range would be nice.

Thanks, in advance, for your help and advice.

-Alan

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