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

[James Harper <james.harper@xxxxxxxxxxxxxxxx>]

> -----Original Message-----
> From: braintorch [mailto:kkabardin@xxxxxxxxx]
> Sent: Sunday, 26 May 2013 9:49 PM
> To: James Harper
> Cc: xen-users@xxxxxxxxxxxxx
> Subject: Re: [Xen-users] Software Raid 5 domu performance drop
> 
> 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

I don't see a block size on the domu measurements... did you just copy and 
paste it wrong or did you really leave it at default 512 byte block size?

James
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