[ovirt-users] Poor guest write speeds

[Alan Murrell]

Hello again.

So I have been doing some more testing just to be sure.  I performed a 
reboot of my Win7 ESXi guest VM between each running of the Parkdale HDD 
speed test app, just to be absolutely sure the results were not a result 
of caching and each time I get pretty consistent results: no less than 
60 MByte/s Seq. Write and around the same for Seq. Read.

In oVirt, is there some tuning I am maybe missing?  Is there a different 
HDD type I should be selecting (or converting to)?

-Alan


On 27/07/2015 6:34 PM, Alan Murrell wrote:
> 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
>>
>>
>
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