Re: [Xen-users] Big I/O performance difference between dom0 and domU

["Liang Yang" <multisyncfe991@xxxxxxxxxxx>]

What is the CPU utilization when you did this I/O performance measurement?
As far I can remember, Bonnie++ does not support using outstanding I/Os.
So your target RAID volume may not be saturated, i.e. you did not get the 
peak
performance.

Liang

----- Original Message ----- 
From: "Marcin Owsiany" <marcin@xxxxxxxxxx>
To: "Xen-Users" <xen-users@xxxxxxxxxxxxxxxxxxx>
Sent: Tuesday, April 17, 2007 8:28 AM
Subject: [Xen-users] Big I/O performance difference between dom0 and domU


> Hi,
>
> I am setting up a dual CPU PowerEdge 2550 system with PERC 3Di
> controller (aacraid) with 3 18GB disks in RAID5 and XEN 3.0.3-0-2,
> credit scheduler, PAE (the Debian package in etch). This is not best
> hardware, but what worries me more is the poor I/O performance in domU
> compared to dom0.
>
> With both domains having 500 MB of RAM, testing with bonnie++ on the
> same 5GB LVM volume with xfs filesystem, with 4GB test data size, I'm
> getting:
>
> -----+-------------------+--------------------+-----------------------
> Test | block read [kB/s] | block write [kB/s] | random seeks [/sec]
> -----+-------------------+--------------------+-----------------------
> dom0 | 10308             | 64806              | 325.3
> domU |  7299             | 53469              | 265.6
> -----+-------------------+--------------------+-----------------------
> ~drop|    30%            |    17%             |  18%
> -----+-------------------+--------------------+-----------------------
>
> The results are basically the same whether I use the default vcpu
> arrangement (2 vcpus for dom0, one for domU) or set it to one vcpu per
> domain, each pinned to a different physical cpu.
>
> Any suggestions are welcome...
>
>
> --
> Marcin Owsiany <marcin@xxxxxxxxxx>              http://marcin.owsiany.pl/
> GnuPG: 1024D/60F41216  FE67 DA2D 0ACA FC5E 3F75  D6F6 3A0D 8AA0 60F4 1216
>
> "Every program in development at MIT expands until it can read mail."
>                                                              -- Unknown
>
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