[ovirt-users] Poor guest write speeds

[Alan Murrell]

Hello,

So a bit of an update, though I still have some additional testing to  
do.  I installed ESXi 5.5 on the same hardware (blew away my oVirt  
install) and installed a Windows 7 VM, with same settings (2GB RAM, 1  
single-core vCPU, 60GB thin-provisioned HDD)

The install of Windows itself was definitely *way* faster.  I don't  
have actual timings for real comparisons, but I can say with 100%  
certainty that the install was faster.  I would say it took at *least*  
half the time to install as oVirt, though to be honest, I would have  
to say it was maybe 1/3 of the time.

Once installed, I installed the VMware Guest Tools, then downloaded  
and ran the "Parkdale" app with the same settings I ran it under the  
Windows 7 VM.  The preliminary results are interesting.

The "Seq. Write" test comes up at around 65 MByte/s, which compares  
well to the bare metal results I got previously.  What is interesting  
(and disappointing) is that the "Seq. Read" test indicates about  
65MByte/s, which is a *huge* decrease to what I was getting in the  
oVirt Win7 guest.

As I mentioned, still going to do some additional testing, but wanted  
to let you know that -- initially, anyway -- the problem under oVirt  
does not seem to be a hardware-related issue, but possibly something  
with the virtio-SCSI?

For those who are running Windows VMs in production, what sort of  
performance do you see?  What type of virtual HDD are you running?

I will post back either later or some time tomorrow (Tue) with more results.

-Alan


Quoting "Alan Murrell" <lists at murrell.ca>:

> 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
>
>