[Xen-users] Impressive Performance Problems with Small-Files /Small Blocksizes

["Balg, Andreas" <a.balg@xxxxxxxx>]

hello everybody,

during some extensive benchmarking for an evaluation we found some issues with 
i/o-performance and also memory bandwidth of Xen 3.4.2 (using XCP-0.5) running
on a quite up-to-date and performant Dell-R610 Server (2 x Xeon E5620, 16G RAM,
4 x SATA 15K HDD's - RAID 5):

- Especially for small block sizes (below 32k) the I/O is very poor. 

to give some figures:  The same Benchmark 
 "time iozone -az -i0 -i1 -i2 -i8 -Rb results.xls"

Runs around 3 Minutes on the bare Hardware, around 30 Minutes in a KVM-VM
and more than 1 hour(!) in a xen VM - See attached graphs and focus on the 
front of the diagram (red and blue "foot" of the xen graph) 

What I'd like to know is, if this is be a glitch in a device driver, an error 
in our configuration or might be eliminated in any other way using a workaround 
or other version.

Or is this a proble of the differences in Design or just nobody noticed it so 
far and it should be lokked at by the developers. Without these two significant 
problems Xen would outperform kvm in almost any possible manner .... 


Best regards 
Andreas



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Disk-IO.png
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RAM-Bandwidth.png
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Time-graph.png
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