RE: [Xen-users] best practices in using shared storage for XEN VirtualMachines and auto-failover?

[Jeff Sturm <jeff.sturm@xxxxxxxxxx>]

> -----Original Message-----
> From: Rudi Ahlers [mailto:Rudi@xxxxxxxxxxx]
> Sent: Friday, October 15, 2010 5:11 AM
> To: Jeff Sturm
> Cc: xen-users
> Subject: Re: [Xen-users] best practices in using shared storage for XEN
> VirtualMachines and auto-failover?
> 
> On Thu, Oct 14, 2010 at 3:42 PM, Jeff Sturm <jeff.sturm@xxxxxxxxxx> wrote:
> > With 2 servers, I hear good things about DRBD, if you don't want to go
> > the SAN route.  If you have a SAN make sure it is sufficiently
> > redundant--i.e. two (or more) power supplies, redundant Ethernet,
> > spare controllers, etc.  And of course RAID 10 or similar RAID level
> > to guard against single-drive failure.
> 
> I am planning on setting up a SAN with a few Gluster / CLVM servers - just 
> need to
> decide which one first, but I'm going to attemp high availability + load 
> balancing +
> ease-of-upgrade-with-no-downtime. Each server will run RAID10 (maybe RAID6?)

Sounds like a fun project.  Never tried Gluster, myself.

> So would you bond eth0 & eth1, and then eth2 & eth3 together? But then 
> connect the
> bonded eth0+1 one one switch, and eth2+3 on another switch for failover? Or 
> would
> you have eth0 & eth2 on one switch, and eth1 &
> eth3 on the other? Is this actually possible?

We generally do the latter.  It's certainly possible, with active-backup 
bonding mode for IP traffic on eth0/1, and multipath for SAN traffic on eth2/3.

The switches are not required to cooperate in this mode (unlike active-active 
or LACP), but should remain connected to one another in case two hosts have 
their active links on different switches. You'll see that happen if you unplug 
a cable on the active link on any host--the backup link will become active for 
that host only.

> I presume the 2 switches should also be
> connected together (preferably via fiber?) and then setup Spanning Tree? Or 
> should I
> seperate the 2 networks,and connect them indivually to the internet?

You wouldn't use spanning tree with bonding--use one or the other.   I've had 
some luck with Linux bridging and spanning tree, but the network delays in 
learning mode may be intolerable.  (Linux bridging has no support for RSTP, 
yet.)

Try it yourself.  I'd encourage you to run your own tests by physically 
unplugging cables and powering down switches before you go into production.

-Jeff



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