Re: [Xen-users] Raid1 performance

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Fri, Apr 09, 2010 at 12:40:39PM +0200, blub@xxxxxxxx wrote:
> > On Fri, Apr 09, 2010 at 11:05:40AM +0200, blub@xxxxxxxx wrote:
> >> > On Thu, Apr 08, 2010 at 08:23:19PM +0200, blub@xxxxxxxx wrote:
> >> >> > On Thu, Apr 08, 2010 at 07:00:11PM +0200, blub@xxxxxxxx wrote:
> >> >> >> hello
> >> >> >> i've been trying to achieve reasonable disk i/o performance on
> >> xen.
> >> >> >> on debian 5.0.4 (xen 3.2.1, kernel 2.6.26) the pv/hvm performance
> >> is
> >> >> >> alright with a raid1 inside the domU. unfortunately the qemu
> >> version
> >> >> >> (0.9.0) does not cover my needs.
> >> >> >>
> >> >> >> so i've been trying xen 3.4.2 & 4.0.0rc8 on gentoo (2.6.31)
> >> >> >> on both versions, the disk i/o performance drops to zero when
> >> copying
> >> >> >> large files. initially the performance is ok (~30mbyte/s) but
> >> drops
> >> >> to
> >> >> >> zero after ~300mb, i've tried it with wget/ftp/scp
> >> >> >> this happens with both PV & HVM domU's. i've tried multiple nic
> >> >> drivers
> >> >> >>
> >> >> >> the performance seems alright if no raid1 is running on the domU
> >> >> >> i cannot run the domU raid1's on the dom0 since there are multiple
> >> >> dom0s
> >> >> >> connecting to multiple FC SAN's and the raid1's are done across
> >> the
> >> >> >> SAN's
> >> >> >>
> >> >> >> (btw, the performance with raid1's on the SAN's is excellent on
> >> dom0)
> >> >> >>
> >> >> >> anyone else has experienced this issue?
> >> >> >>
> >> >> >
> >> >> > Did you make sure dom0 has more weight than the domUs, so that it
> >> is
> >> >> able
> >> >> > to process the IO requests?
> >> >> >
> >> >> > See: http://wiki.xensource.com/xenwiki/XenBestPractices
> >> >> >
> >> >> > -- Pasi
> >> >> >
> >> >> >
> >> >>
> >> >> yes, the box has 8 physical cores, and the domU test installation
> >> only
> >> >> uses two of them
> >> >>
> >> >
> >> > How many cores does dom0 have?
> >> > Did you set up the xen credit scheduler weights?
> >> > Did you pin the vcpus to specific cores?
> >> >
> >> > What does "iostat 1" show in dom0 while you run the test?
> >> > What does "xm top" show in dom0 while you run test?
> >> >
> >> > -- Pasi
> >> >
> >> >
> >>
> >>
> >> here is the output: http://pastebin.com/c3JqU7e4
> >>
> >> everything looks normal in my opinion
> >>
> >
> > Dom0 should have more weight than the domU!
> >
> > Was that dstat from domU or from dom0?
> >
> > -- Pasi
> >
> >
> > _______________________________________________
> > Xen-users mailing list
> > Xen-users@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-users
> >
> 
> dom0 hast weight 1024, domU 512
> 
> here is iostat within domU:
> http://pastebin.com/0mHy8Fm1
> 

Ok, so the iowait is huge in the domU.

The question is why? 

Is there iowait in dom0, if you run "iostat 1" there? 

-- Pasi


_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users