WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-users

Re: [Xen-users] Advice on redundant SAN/NAS storage for Xen

To: Xen User-List <xen-users@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] Advice on redundant SAN/NAS storage for Xen
From: "Fajar A. Nugraha" <fajar@xxxxxxxxx>
Date: Sat, 30 May 2009 12:30:22 +0700
Delivery-date: Fri, 29 May 2009 22:31:07 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <4A2045DB.4090107@xxxxxxxxxxxxxx>
List-help: <mailto:xen-users-request@lists.xensource.com?subject=help>
List-id: Xen user discussion <xen-users.lists.xensource.com>
List-post: <mailto:xen-users@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-users>, <mailto:xen-users-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-users>, <mailto:xen-users-request@lists.xensource.com?subject=unsubscribe>
References: <4A2045DB.4090107@xxxxxxxxxxxxxx>
Sender: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
On Sat, May 30, 2009 at 3:30 AM, Chris 'Xenon' Hanson
<xenon@xxxxxxxxxxxxxx> wrote:
>  I'm planning to expand my Xen servers at my datacenter into a cluster with 
> high
> availability and reliability. As part of this, I want to move all DomU 
> storage to a common
> SAN or NAS infrastructure and make all the Dom0s basically identical. In this 
> way, I can
> move DomU's around between Dom0s as needed for performance or reliability 
> reasons. If a
> Dom0 server fails, I can just bring up its DomUs on different servers with no 
> loss.

Simple goal, not-so-simple implementation.

>  The best design I can think of is this:
>
> Two machines running Linux configured as SANs, using something like ATA over 
> Ethernet
> (AoE) to link them to a pair of GigE switches that then link to every Dom) 
> box. The pair
> of SAN boxes each export a block of raw storage that the Dom0 machine then 
> RAIDs together
> as RAID1 and provides to Xen and the DomU as a block device. The Dom0 gets
> network-portable storage, with RAID reliability and redundancy.
>
>  The other way might be to have the Dom0 and Xen pass through both block 
> devices to the
> DomU and let the DomU RAID them together. I'm not sure if either is better. 
> Maybe RAID on
> the DomU would allow the DomU to be migrated easier?

RAID might be the weakest link here. Think what will happen if :
- one of the SAN box gets disconnected -> RAID will (hopefully) cope
with it well and use the live SAN
- some time later, the dead SAN is available again -> RAID won't
automatically re-add it
- the other SAN dies.

These are big IFs, but you get the idea.

>
>  Is there a better and less messy way to provide redundant SAN-type storage 
> to Xen DomUs?
> The main criteria are:
>
>  Immune to failure of a single switch or SAN box.
>  Allow DomUs to be moved seamlessly to other Dom0s without messy 
> reconfiguration.

Immune to a SAN box failure is hard.
The common way to do it in enterprise-level storage is to have high
availability in the SAN box. It does raid and have multiple
controllers in a cluster/HA setup so that it'd be "immune" enough to
disk or controller failure. I don't think there's a viable way to
achieve that with your planned setup. Feel free to correct me if I
wrong.

-- 
Fajar

_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users