VMware and HA solutions

Michele Donna michele.donna at arxis.it
Mon Mar 10 11:18:11 MET 2008


Hi,

thanks for your explanation!

since also on "real" hardware when a host dies there is a
downtime due to application restart on the failover host, my
concerns are related to "who" will manage application
failover..for example I would not recommend to just put
startsap commands in runlevel boot scripts ;)

on the other side I would sleep safe when thinking that
there is a monitoring agent that is able (or should so..) to
recover my instances automatically.

thanks and regards,
Michele






----- Original Message -----
Da : Marco Wiese <mwiese at beit.de>
A : <linux.general at listserv.sap.com>
Oggetto : RE: VMware and HA solutions
Data : Mon, 10 Mar 2008 11:02:45 +0100

> Hi,
> 
> VMWare HA is associated with a short downtime. Don't mix
> up HA and DRS:
> 
> HA: If you have an HA cluster (e.g. with 3 ESX hosts) and
> one host gets  isolated from network or goes down, HA will
> just boot the VMs on the other  both ESX hosts. Be aware,
> in this case you have a downtime! If one ESX  host dies,
> there is no chance to rescue the memory of the VMs, so
> they are  lost. For high availibilty they get started
> immediately on the other  hosts. In case of network
> isolation you can configure each virtual  machine, what to
> do. If you really loose your network (interfaces), the 
> virtual machines are up and running, but they can't be
> accessed from  network. So ESX gives you the opportunity,
> to shutdown and reboot your VM  (in order to boot on
> another ESX host to get access to the network again)  or
> stay running on the isolated ESX host.
> 
> DRS: This feature moves the virtual machine in running
> state to another  ESX host. In that case, no one will
> notice, your machine has moved. This  feature is to
> prevent high load on the ESX hosts in a cluster, so you
> have  a load balance all over your hosts. If one virtual
> machines gets heavy  load or memory allocation, the other
> virtual machines on that ESX host  will move to the other
> hosts in the cluster. You can configure this  feature in
> different gradations to be flexible with your load
> balancing  (regarding the number of hosts in your
> cluster).
> 
> I hope, you understand now, HA is not for high availibilty
> meaning, you  have no downtime. In case you have! But your
> virtual machines become up  and running in a few minutes
> after crash or network isolation.
> 
> Regards
> Marco
> 
> 
> "Michele Donna" <michele.donna at arxis.it> schrieb am
> 10.03.2008 10:35:23:
> 
> > [Bild entfernt] www  Diese EMail erreichte Sie via
> > Internet... /  This mail was sent via internet...
> > 
> > Hi,
> > 
> > What I'm trying to understand is if we can manage SAP
> > instances simply using VMware HA tools or if we have to
> > use another layer of ha software just for SAP.
> > 
> > If VMware HA can provide a sort of Business continuity
> > solution that's fine for us.. 
> > 
> > 
> > thanks and regards,
> > Michele
> > 
> > ----- Original Message -----
> > Da : "Euler, Christian" <euler at aov.de>
> > A : <linux.general at listserv.sap.com>
> > Oggetto : RE: VMware and HA solutions
> > Data : Mon, 10 Mar 2008 08:58:56 +0100
> > 
> > > Hi,
> > > 
> > > ESX is capable of migrating virtual machines on the
> > > fly between two hosts. I'm not sure if a guest system
> > > is able to trigger a migration itself (by using the
> > > vmware tools for example), or if you need an external
> > > solution for such a HA setup. 
> > > 
> > > There's no downtime and your users won't notice the
> > > switch , because the migration process creates a
> > > shadow instance of the running guest in the target
> > > system and then only needs a few seconds to switch
> > > over network connection etc. 
> > > If you're using SLES10, the combination of Xen and
> > > Linux-HA could be a another solution for a clustered
> > > setup. We're currently evaluating this, and it seems
> > > that Xen causes less overhead than VMWare.
> > > 
> > > Regards,
> > > Christian Euler
> > > 
> > > AOV IT.Services GmbH
> > > Bartholomäusweg 32
> > > 33334 Gütersloh
> > > Tel. +49 (5241) 9463-101
> > > Fax +49 (5241) 9463-55
> > > eMail euler at aov.de
> > > http://www.aov.de
> > > 
> > > Handelsregister: Amtsgericht Gütersloh HRB 1265
> > > Aufsichtratsvorsitzender: Bülent Uzuner
> > > Geschäftsführung: Hans-Georg Oeser/Peter
> > Schulte-Rentrop
> > > 
> > > 
> > > "With sufficient thrust, pigs fly just fine. However,
> > > this is not necessarily a good idea. It is hard to be
> > > sure where they are going to land, and it could be
> > > dangerous sitting under them as they fly overhead."
> > > (RFC 1925) 
> > > 
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