Re: [Xen-users] Software Raid 5 domu performance drop

[James Harper <james.harper@xxxxxxxxxxxxxxxx>]

> 
> 26.05.2013 14:43, James Harper ÐÐÑÐÑ:
> >> Hello. I'm experiencing solid I/O performance drop when using software
> >> raid 5 from PV DomU. I can get about 420M/s for sequential reads and
> >> ~220 M/s for sequential writes when using it from Dom0. But it's only
> >> ~170 M/s for read and ~80 M/s for write when using it from DomU.
> >>
> >> DomU performance for single drive is close to native â ~160 M/s for
> >> reads and ~160 for writes.
> >>
> >> There is no filesystem or LVM, just raw data. Debian wheezy x86_64 for
> >> both Dom0 and DomU. And "phy" backend is used to attach drive to
> DomU.
> >> Is this a bug or something wrong with my setup? What should I check?
> >>
> > How are you measuring this performance?
> >
> > James
> I  running dd if=/dev/zero of=/dev/xvdb bs=1M for several minutes.
> 
> Also tried "cat /dev/zero | pv -r > /dev/xvdb " which gave me similar
> results.

Add oflag=direct to the dd command so that no caching is in effect and then 
compare.

James
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