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Re: [Xen-users] Speed of Xen Network Bridge Interface (10/100/1000?)

To: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
Subject: Re: [Xen-users] Speed of Xen Network Bridge Interface (10/100/1000?)
From: Stephan Seitz <s.seitz@xxxxxxxxxxxx>
Date: Wed, 28 Nov 2007 07:25:58 +0000
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Just to add some salt to the original posters question, I'm going to migrate
clustermembers into domU's on one big machine.
Well, it's not a full featered HA cluster, it consists of one huge nfs/nis
server and a lot of diskless servers with as little as necessary failover
First tests showed, that booting one of the machines as domU results in
random disk throughput of about 10 MB/s against about 80-95MB/s when running
on bare-matel.
I don't necessarilly need to keep the current infrastructure, but I'll 
need one mountpoint available on many (expandable) machines.
Is there some best-practice description on how to get one mountpoint available 
a lot of domU's ?

Thanks for any suggestion!


Mark Williamson schrieb:
>> I would like to learn the speed of the network bridge interfaces created by
>> XEN.
>> More specifically, on xenbr0, given that the traffic only occurs between my
>> Dom0 host and PV DomU guest, am I limited to 10 Mbps, 100 Mbps or 1000
>> Mbps? Does it depend on something such as ethernet card capability (even
>> though the packets don't go out of the card and stay inside Dom0)?
> It's not limited by your physical ethernet card, nor is it restricted to any 
> particular maximum.  It's basically limited by how fast the Xen virtual 
> network drivers and the Linux bridging code can move the data around.  This 
> used to actually be slower a domU accessing the physical ethernet due to the 
> extra memory operations that were required (and used a fair bit of CPU).  I 
> think there have been some changes to reduce the bottleneck and improve 
> intrahost performance since then, so it would be faster than I remember it.  
> I'm not sure if it's currently faster than GigE; possibly.
> It ought to be significantly faster than 100Mbps on a modern machine.  It'll 
> act like a really fast ethernet card, with no hard limit on the transmission 
> speed (instead, transmission speed will be limited by how powerful your 
> machine is and how efficient the virtual ethernet code is).
>> I plan to use iScsi or Ata-over-Ethernet, that's why I'm asking this
>> question,
> Is that from dom0 to domU?  Do you have a particular reason for doing that?  
> Using blkback / blkfront would be simpler and more efficient.
> Cheers,
> Mark

Stephan Seitz
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