From mboxrd@z Thu Jan  1 00:00:00 1970
From: Anthony Liguori <anthony@codemonkey.ws>
Subject: Re: qcow2 slowdown in kvm-78,79
Date: Wed, 19 Nov 2008 12:26:41 -0600
Message-ID: <49245A61.9050504@codemonkey.ws>
References: <1227019192.22098.4.camel@henrik-desktop> <20081119182317.GA31893@us.ibm.com>
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Cc: Henrik Holst <henrik@witsbits.com>, kvm@vger.kernel.org
To: Ryan Harper <ryanh@us.ibm.com>
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Ryan Harper wrote:
> * Henrik Holst <henrik@witsbits.com> [2008-11-18 08:42]:
>   
>> The bundled qemu in kvm-78 and kvm-79 slows down disk i/o with qcow2
>> images by an order of 10. If one got 60MB/s before, one gets around
>> 6MB/s with 78 and 79 (measured with dd)
>>     
>
> dd command?
>
> what's your -drive parameters look like, specifically, what if type?
> ide, scsi, virtio?
>   

This is probably the change to cache=writethrough.  I bet if you set 
cache=writeback then you'll see this go away.

qcow needs some love.

Regards,

Anthony Liguori