Re: Two redundant Xen servers with one SAN

[mabi <mabi@xxxxxxxxxxxxx>]

Thanks Florian and GD for your answers.

I should have been more precise, I am looking into building a active/passive 
dual node Xen installation. I don't need active/active as I believe this is 
also more dangerous.

Also I was thinking that I would manually failover the VM whenever necessary in 
order not to rely on additional external tools such as corosync/pacemaker and 
hence avoid more complexity.

So as you notice, at least for a start, I am trying to keep things as simple as 
possible. If I understand correctly that should be possible with Xen and all I 
need is multipathd and CLVM, is this correct?

Then regarding CLVM, I checked Debian buster but could not find any 
CLVM-related pacakges. Is maybe CLVM not available on Debian?

Regards,
Mabi

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐

On Thursday, June 24th, 2021 at 12:28 PM, Florian Heigl 
<florian.heigl@xxxxxxxxx> wrote:

> Hi,
>
> you can look into solutions based on cLVM or OCFS2 + Corosync/Pacemaker.
>
> Don't forget to set up multipathd so your system can handle the 
> link/controller failovers.
>
> This has been done, and also has been/is a commonplace solution. There is 
> also lots of blog posts that you can dig up once you search the right way.
>
> I would avoid running natively on SAN luns attached to VMs due the risk of 
> "the cluster stack had an error / was misconfigured". If you'd failover 
> manually that would be less of an issue. The clusters like Pacemaker can 
> protect the VMs a bit using SCSI reservations.
>
> There was also Remus for running 2 VMs in lockstep for HA, but that was 
> expecting no shared storage and was never polished by anyone to be worthwhile 
> for production use.
>
> A fair warning: Most homegrown HA setups like they're done commonly in the 
> ISP industry tend to blow up much more often than what a proper solution 
> should be like.
>
> It might be better to pick something pre-made for that purpose if you don't 
> have the SAN/Cluster experience.
>
> I.e. XenServer/XCP or Oracle VM3.
>
> Good luck!
>
> Florian
>
> > Am 24.06.2021 um 10:09 schrieb mabi mabi@xxxxxxxxxxxxx:
> >
> > Hello,
> >
> > Is it possible with Xen on Debian 10 to have two Xen servers both directly 
> > attached in a redundant way through HBA interfaces to a single SAN?
> >
> > The goal here would be to achieve higher availability of the Vms in case 
> > one Xen server is down for maintenance or because it is defective. This 
> > would mean that the the virtual machines can continue to run on the second 
> > available Xen server. The SAN would be used to store the virtual machines 
> > images directly via LVM I guess.
> >
> > I did not find any Xen documentation or third-party howtos in order to do 
> > that. Does anyone have any pointers to some documentation or hints? or 
> > maybe this is simply not possible?
> >
> > Best regards,
> >
> > Mabi