Re: Two redundant Xen servers with one SAN

[Florian Heigl <florian.heigl@xxxxxxxxx>]

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
> 
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