CentOS virt - Jul 2015 - Live migration using shared storage in different networks

Hi!

I am building a KVM cluster that needs VM live migration.

My shared storage as well as the KVM hosts will be running
CentOS.

Because 10 Gbps Ethernet switches are very expensive at the
moment I will connect the KVM hosts to the storage by
cross-over cables and create private networks for each
connection (10.0.0.0/30 and 10.0.0.4/30).

The following diagram shows the topology

 Management             Management            Management
    VLAN                   VLAN                  VLAN
     |                      |                     |
+----+-----+  10 Gbps  +----+----+  10 Gbps  +----+-----+
| KVM Host |-----------| Storage |-----------| KVM Host |
+----+-----+           +----+----+           +----+-----+
     |                      |                     |
   Public                 Public                Public
    VLAN                   VLAN                  VLAN

My question is: will live migration work in this configuration
since the storage will have 2 different IP addresses
(10.0.0.1 and 10.0.0.5) in 2 different networks even though
it is the same storage?

Thanks!

A couple of comments.

Take a look at http://whiteboxswitch.com/ or do a general search for 
white box switches.


Migration will work so long as the storage is consistent between the two 
KVM hosts.
If there is buffering or caching going on you could have problems.
Something like GFS or NFS will work.
I have used DRBD to setup a simple 2 node system and migration works 
quite nicely.

Take a look at ProxMox or some of the postings on alteeve.ca.
A good place to start would be
https://alteeve.ca/w/2-Node_Red_Hat_KVM_Cluster_Tutorial


On 07/06/2015 07:58 AM, Miguel Barbosa Gon?alves wrote:
> Hi!
>
> I am building a KVM cluster that needs VM live migration.
>
> My shared storage as well as the KVM hosts will be running
> CentOS.
>
> Because 10 Gbps Ethernet switches are very expensive at the
> moment I will connect the KVM hosts to the storage by
> cross-over cables and create private networks for each
> connection (10.0.0.0/30 and 10.0.0.4/30).
>
> The following diagram shows the topology
>
>   Management             Management            Management
>      VLAN                   VLAN                  VLAN
>       |                      |                     |
> +----+-----+  10 Gbps  +----+----+  10 Gbps  +----+-----+
> | KVM Host |-----------| Storage |-----------| KVM Host |
> +----+-----+           +----+----+           +----+-----+
>       |                      |                     |
>     Public                 Public                Public
>      VLAN                   VLAN                  VLAN
>
> My question is: will live migration work in this configuration
> since the storage will have 2 different IP addresses
> (10.0.0.1 and 10.0.0.5) in 2 different networks even though
> it is the same storage?
>
> Thanks!
> _______________________________________________
> CentOS-virt mailing list
> CentOS-virt at centos.org
> http://lists.centos.org/mailman/listinfo/centos-virt

-- 
Alvin Starr                   ||   voice: (905)513-7688
Netvel Inc.                   ||   Cell:  (416)806-0133
alvin at netvel.net              ||

On Mon, Jul 6, 2015 at 7:58 AM, Miguel Barbosa Gon?alves <m at mbg.pt>
wrote:
> Hi!
>
> I am building a KVM cluster that needs VM live migration.
>
> My shared storage as well as the KVM hosts will be running
> CentOS.
>
> Because 10 Gbps Ethernet switches are very expensive at the
> moment I will connect the KVM hosts to the storage by
> cross-over cables and create private networks for each
> connection (10.0.0.0/30 and 10.0.0.4/30).
>
> The following diagram shows the topology
>
>  Management             Management            Management
>     VLAN                   VLAN                  VLAN
>      |                      |                     |
> +----+-----+  10 Gbps  +----+----+  10 Gbps  +----+-----+
> | KVM Host |-----------| Storage |-----------| KVM Host |
> +----+-----+           +----+----+           +----+-----+
>      |                      |                     |
>    Public                 Public                Public
>     VLAN                   VLAN                  VLAN
>
> My question is: will live migration work in this configuration
> since the storage will have 2 different IP addresses
> (10.0.0.1 and 10.0.0.5) in 2 different networks even though
> it is the same storage?
>
I don't know for sure if you'll run into problems having two different
IP
addresses, but I'd suspect you would.
Some people (myself included) on this list use LVM backing and DRBD on the
KVM hosts in which case the referenced storage layer is identically named.

Solution(?) for your scenario:
Maybe create a bridge on your Storage node that includes both 10Gbit NICs
going to your KVM hosts?
That way you put a single IP address on the bridge and it is accessible
(because it's bridged) to both KVM hosts. And less need for a 10Gbit switch
(just yet).


-- 
---~~.~~---
Mike
//  SilverTip257  //
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