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

[braintorch <kkabardin@xxxxxxxxx>]

26.05.2013 15:16, James Harper ÐÐÑÐÑ:
> > 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
James, it's even more dramatic without caching.


Dom0:

Reading:
dd if=/dev/md0 of=/dev/null bs=1M iflag=direct
 ÑÐÐÐÐÑÐÐÐÐÐ 11659116544 ÐÐÐÑÐ (12 GB), 27,4614 c, 425 MB/c

Writing:
dd if=/dev/zero of=/dev/md0 bs=1M oflag=direct
 ÑÐÐÐÐÑÐÐÐÐÐ 10108272640 ÐÐÐÑ (10 GB), 135,859 c, 74,4 MB/c

Domu:

Reading:
dd if=/dev/xvdb of=/dev/null iflag=direct
 ÑÐÐÐÐÑÐÐÐÐÐ 229615104 ÐÐÐÑÐ (230 MB), 75,9394 c, 3,0 MB/c

Writing:
dd if=/dev/zero of=/dev/xvdb oflag=direct
 ÑÐÐÐÐÑÐÐÐÐÐ 231818240 ÐÐÐÑ (232 MB), 158,283 c, 1,5 MB/c

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