[PVE-User] What is the purpose of second gluster server in storage config?

[Thomas Lamprecht]

On 4/6/19 8:39 AM, Igor Podlesny wrote:
> -- Beyond of the obvious "well, it's for redundancy". That's obvious..
> but "What subsystems and under what circumstances are gonna use it?"
> -- isn't at all.
> 
> I have strong suspicion that qemu-kvm isn't capable of fail-over
> switching in case its primary gluster server went down. At least
> preliminary tests showed that on single node's (that is a part of
> replicated gluster cluster setup) failure VM's disks are gone
> (effectively are kinda pulled off for VMs).
> 
> Second server's IP isn't even seen among arguments of kvm process.
> 
> Moreover, /proc/mounts doesn't even contain any mention of
> backup-volfile-servers or similar options.
> 


Quite a bit ago QEMU only supported a single server when passing a
GlusterFS backed volume, thus Proxmox VE tries to bing both set servers
on the relevant GlusterFS ports and passed the first one available.

Then, some QEMU releases ago, support for passing multiple GlusterFS
servers was added to QEMU, which it now uses to failover.
Nobody changed our QEMU interface to adapt to that new, even better
possibility..

maybe it came from the fact that the more scalable and better integrated
ceph was already on the plate, and GlusterFS usage in PVE declined a bit,
maybe it just wasn't noticed by GlusterFS users, thus nobody stepped up or
made much noise changing that. Anyway, I'd be open for patches regarding
this.

cheers,
Thomas