Re: [Xen-users] disk backend performance

[Thomas Halinka <lists@xxxxxxxxx>]

Hi Stefan,

Am Freitag, den 28.11.2008, 15:41 +0100 schrieb Stefan de Konink:
> On Fri, 28 Nov 2008, Thomas Halinka wrote:
> 
> > Am Freitag, den 28.11.2008, 10:54 +0100 schrieb Stefan de Konink:
> > > On Fri, 28 Nov 2008, Guillaume wrote:
> > >
> > > > I ask me some questions about xen disk backend performance. What is the
> > > > better backend to use to have the best ones.
> > > >
> > > > For me I tought its better to use phy: than disk: , because it's does'nt
> > > > need "encapsulation" to store data in and so, writing data is quicker. 
> > > > But
> > > > maybe i'm wrong.
> > > > Maybe some of you can give advise and more info about that !
> > >
> > > iSCSI + pvSCSI seems to be optimal I guess.
> >
> >
> > iSCSI is pretty slow, because of all the tcp-ip overhead. Try AoE since
> > its Layer 2 (Ethernet)
> 
> Please come with benchmarks,

i do not need any benchmarks. i measured that iscsi could saturate a
GB-Link with about 55-60% - AoE was about 80-85% at less CPU-Usage!

Why is FC faster than iSCSI? Ah, it s because of the protocol.

and why?
Because FC is layer2 like AoE
and iscsi is layer 3/4 - so much more protocol-overhead has to
processed.


>  and preferably stability comparisons.

open-iscsi has no stable releases yet. aoetools do have. There are also
many users complaining about iscsi-kernel-issues....

Just search the net for iscsi.problems on linux. 
>  Never
> the less, AoE would still process on dom0, while pvSCSI is directly done
> on the domU.

yep.

> Stefan

Thomas

[1] http://www.apac.edu.au/apac07/pages/program/presentations/Tuesday%
20Harbour%20C/Antony%20Gerdelan.pdf
[2] http://www.linuxdevices.com/news/NS3189760067.html



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