Re: [Xen-API] XCP 1.1 - poor disk performance, high load and wa

[Denis Cardon <denis.cardon@xxxxxxxxxxxxxxxxxxxxxx>]

Hi George,

> By default XCP 1.1. does not support software raid.
> 
> Under certain condition you can use is, but you need to know you
> going
> do deep water. And it's better to know how to swim... I mean,
> understand
> internals of XCP.
> 
> If you are 'just a user' - do not use software raid.
> 
> If you wish some help here -  say which device (virtual or real) is
> bottleneck.

first thank you for the dedicated time you spend on the xcp mailing list. It is 
definitly a big advantage for the project to have a dynamic mailing list.

I've come across the slow md raid5 issue with a XCP 1.1 a month ago, and didn't 
have much time to look into it since it is a non production small dev/test 
server and I'm using hardware raid on production servers. 

Like the initial poster's mail, on my dev server io write access goes to hell 
and loadavg skyrockets even with very light disk write. However the behavior is 
not consistent with a standard io staturation since parallel io access are not 
much affected... That is to say that I can launch a "iozone -a -n512m -g512m" 
on a 256MB VM and at the same time a "find /" still goes thought quite 
smoothly... Using vmstat on dom0 sometime I saw up to 60k blocks per seconds 
(4k block I guess) so thoughput seems to be acceptable some time. Note : I'm 
activated cache on the SATA disk (I know, bad idea for production but ok for me 
for dev). I've not experienced such behavior with installation with hardware 
RAID. 

If I have some time this week, I'll try to convert the setup with ext3 
partition (thin provisioning) to be able to make iozone directly on the SR. I 
know md soft RAID is not a supported configuration, and I agree it should not 
be unless the sata disk cache is deactivate (which gives bad performance). 
However in some very small setup or dev setup, it might still be interesting.

Cheers and keep on the good work!

Denis

> 
> 
> On 16.09.2012 20:43, SpamMePlease PleasePlease wrote:
> > All,
> >
> > I've installed XCP 1.1 from latest available ISO on Hetzner's 4S
> > server with usage of md raid 1 and LVM for local storage
> > repository.
> > The problem Im seeing is extremely poor disk performance -
> > importing
> > vm file that was exported in ~3m from another XCP 1.1 (also
> > Hetzner's
> > server, but bit older one, EQ6) takes up to 2 hours, and in
> > meantime
> > the dom0 becomes almost unusable, the load goes up to 2, it has
> > constant 50% (or higher) of wa(it) and is extremely sluggish.
> >
> > Now, I wouldnt mind the sluggishness of dom0, but 2h for vm import
> > seems crazy and unacceptable. I've made multiple installations of
> > the
> > server to make sure I am not doing anything wrong, but the same
> > setup
> > works flawless on older machine. I've tested the drives and they
> > seem
> > to be fine, with up to ~170mb/s throughtput on SATA3.
> >
> > Is there anything else I can check to see if its hardware problem,
> > or
> > anything that could be configured on dom0 to make it operational
> > and
> > usable?
> >
> > Kind regards,
> > S.
> >
> > _______________________________________________
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> > Xen-api@xxxxxxxxxxxxx
> > http://lists.xen.org/cgi-bin/mailman/listinfo/xen-api
> 
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