[Xen-users] Re: Xen on openmosix/openssi..

[Chris de Vidal <chris@xxxxxxxxxx>]

Forgive me if I sent this twice, I think I hit the "send" button by mistake.

--- Bj�rn Tore Svinningen <bt@xxxxxxxxx> wrote:
> I've seen your post on xen's forum about running Xen ontop of openssi.
> 
> Have you got'en any further on this idea ? Had the same idea myselves, 
> but it seems all posts I find end nowhere.

Hm, I thought this question was answered.

No, you cannot because Xen is a hypervisor.  As I understand it (in my limited 
knowledge), a
hypervisor is a special kernel that sits between the hardware and all OSes, 
even the "host" OS
(called Domain0 in Xen).  The OpenSSI kernel cannot be placed underneath that 
-- it appears to be
an engineering impossibility.  A hypervisor *must* talk directly to the 
hardware; that's what
makes it so fast.

As an alternative, you can do it the other way around; you can run OpenSSI on 
top of Xen:
http://openssi.org/cgi-bin/view?page=docs2/1.9/debian/xen-howto.txt


I have begun to explore using Heartbeat+DRBD instead.  Install Xen, install 
DRBD into Dom0,
synchronize your DomUs on the DRBD partition, install Heartbeat, create another 
node like the
first, use a script to stop/start the DomUs during a failover.  Refer to 
Linux-HA.org or the
xen-users archives for more details.

This is active/passive highly availablity.  If you run DomUs on both nodes and 
create two DRBD
partitions (one for each node) you can make effective use of your hardware and 
get active/active
high availability, which is gives you crude load balancing.  More like load 
levelling, but good
enough for me.  I would prefer not to have a "hot standby" wasting CPU cycles; 
I would rather put
both nodes to work.

Of course if you really require true load balancing you can also run something 
like LVS
(LinuxVirtualServer.org) as a front-end to your many Xen DomUs.

Heartbeat+DRBD+Xen scales out VERY WELL; if you need more processing power or 
RAM, add another
pair of Heartbeat+DRBD+Xen hosts and migrate the existing DomUs to that.  
Virtualization software
such as Xen makes moving servers around to different hosts VERY simple.

I think you'll find that Heartbeat+DRBD+Xen is a great alternative to running 
Xen on top of OpenSSI.

CD

Are you good enough?
TenThousandDollarOffer.com

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