RE: [Xen-users] Windows Disk performance

["Geoff Wiener" <gwiener@xxxxxxxxxxxxxxx>]

Hi Russ;

I have to do disk performance all the time and I use IOmeter heavily.
Have a look at this article:

http://blogs.orcsweb.com/jeff/archive/2008/01/09/disk-usage-and-capacity
.aspx

The author explains how you can use Microsoft (Sysinternals) Diskmon to
capture your existing workload (the one generated by the database
application you want to simulate) and then helps you to calculate that
specific workload in IOmeter.  Once configured you can try out your
workload with various disk configurations / SAN's etc without having to
build your database application on top of every possible scenario.  It
even provides a spreadsheet to convert all the data into the correct
parameters that you need to feed into IOmeter.  It lets you get through
a bunch of "what if's" quickly.  I recently used this to isolate a
problem with an application that uses Microsoft SQL 2000 that started to
misbehave after a SAN upgrade.  We quickly determined that moving the
SQL database from a SAN with Write Back caching enabled to one with
Write Through Caching had a massive performance impact based on the way
the app writes data, not the amount of data being written.  It just
happened to be the way the app needed to use the disk.

My advice is that if you really want to know how something in particular
is going to perform in a new environment, capture the workload
characteristics and then play them back in that environment.  I recently
sent some performance stats to the list for the PVGPL 0.9.5 drivers that
include the workload I'm describing.  I will run the same tests again
now that James has released 0.9.7 along with the iometer configuration.
Also be careful when publishing performance stats not to violate
anyone's EULA.  I know VMware, in particular, are sticky about that :-).

Best Regards

Geoff


-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Ruslan Sivak
Sent: 07 June 2008 5:29 PM
To: James Harper
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Windows Disk performance

James Harper wrote:
>> I've been getting disappointing results on IO reads when using
windows
>> guests.  I'm getting usually around 70MB/s reads using hdtune.  When
>> installing James' PV drivers, the speed drops to about 20MB/s.
>>
>> The host system is getting around 350MB/s reads.  I'm wondering if
>>     
> there
>   
>> is such a significant slowdown, or if my tests are somehow flawed.
>>     
> The
>   
>> 70MB/s persisted throughout my VM testing, whether I was using Xen,
>> XenSource or VMWare Server.
>>
>> So my questions are:
>>
>> a.  Is there a bottleneck somewhere which basically caps the windows
>> disk performance?
>> b. Is my testing methodology flawed.  Is there a better windows tool
>> that will measure performance?  What about Linux tool?  I'm currently
>> using hdparm -t
>>     
>
> If you are using the same tool in Windows then I'm comfortable that a
> drop from 70MB/s to 20MB/s indicates a major problem somewhere.
>
> Actually, since I haven't implemented any of the event log stuff yet
as
> per my last email, could you run DebugView from sysinternals and see
if
> any logging comes up while you run your performance tool? Make sure
> kernel logging is on - you can tell if it is if you go into disk
> management and a whole lot of debug info gets output.
>
> James
>
> _______________________________________________
>   

I will try this on Monday.  Do you know how to turn kernel logging on if

it's not? 

This thread was actually more about why I'm getting such poor perceived 
performance under the stock drivers.  I understand that there may be 
some issues to work out with the PV drivers, but I wouldn't have 
expected such a huge hit of performance across the board with the stock 
drivers (And across the board I mean, Xen, XenServer and VMWare).  
Should I try testing with something like IOmeter?  I'm really more 
interested in db type performance, so maybe a real benchmarking package 
is necessary.  You know the kind that Tom's Hardware uses to measure 
performance?  Does anyone know of any good ones?

Russ

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