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Re: [Qemu-devel] Very poor IO performance which looks like some design p


From: Paolo Bonzini
Subject: Re: [Qemu-devel] Very poor IO performance which looks like some design problem.
Date: Mon, 13 Apr 2015 15:53:10 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0


On 13/04/2015 14:28, ein wrote:
> 
> 
> Check out my update please:
> http://lists.nongnu.org/archive/html/qemu-devel/2015-04/msg01318.html
> 
> Using aio=native,cache=none results in 500%-2000% performance drop
> comparing to bare metal and 300%-1000% comparing to
> aio=threads,cache=unsafe.

Not a surprise that aio=threads,cache=unsafe is faster.  With
cache=unsafe you're telling QEMU that it's okay to lose data in case of
a host power loss.  Same for ext2 over XFS (ext2 isn't even journaled!).

Thus, use XFS and preallocate storage using the "fallocate" command.

Paolo



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