[CentOS-virt] disk i/o benchmarking inside vm

Mon Oct 10 19:14:18 UTC 2011
Stoyan Marinov <stoyan at marinov.us>

Sorry, reply to wrong email :)

On Oct 10, 2011, at 10:08 PM, Stoyan Marinov wrote:

> OK, I think I managed to fix it. Please check and let me know.
> 
> Stoyan
> 
> On Oct 10, 2011, at 9:43 PM, Dennis Jacobfeuerborn wrote:
> 
>> On 10/10/2011 08:27 PM, Nehemiah wrote:
>>> but thats what I'm asking you to investigate. All you see is a symptom,
>>> more data may clarify the situation. Weren't you taking data from both
>>> inside the guests an on the host's disks. It was kind of unclear.
>> 
>> The guest number are the ones that are not consistent with each other or 
>> across restarts of the guests:
>> 
>> seekmark:
>> guest 1: 120 seeks/s
>> guest 2: 220 seeks/s
>> 
>> "hdparm -t" shows:
>> guest 1: 100 MB/s
>> guest 2: 160 MB/s
>> 
>> The host numbers are the ones of the physical drives:
>> seekmark:
>> /dev/sdb: 75 seeks/s
>> /dev/sdc: 75 seeks/s
>> 
>> hdparm -t:
>> /dev/sdb: 140 MB/s
>> /dev/sdc: 140 MB/s
>> 
>> The physical numbers are consistent and what I would expect to see from the 
>> sata drives.
>> The guests are minimal centos 6 installations so after booting they have 
>> virtually no processes running that could influence the benchmarks in any 
>> significant way. The hosts system is installed on /dev/sda so /dev/sd(b|c) 
>> are not influenced by the host system either.
>> The entire setup is arranged to make benchmarking mostly reliable.
>> If there were minor temporary fluctuations I would blame some external 
>> process but differences of almost 100% that are consistent for the lifetime 
>> of the virtual machine do not fit such a scenario.
>> 
>> Regards,
>>  Dennis
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>> CentOS-virt at centos.org
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> 
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