[pve-devel] Two-Node HA

Andreas Steinel a.steinel at gmail.com
Wed Sep 28 17:53:05 CEST 2016


Hi Thomas,

Thank you for your time and your answer.

I wonder why e.g. an Oracle Real Application Cluster (RAC) works so
well with a 2 node in a HA setup. We deployed 50+ clusters in the last
years and never had a split-brain-like situation. Rolling-updates, as
well as occasional host crashes are also possible without loosing data
- sometimes even sessions. If you use Transparent Failover (TAF), your
database sessions will be migrated to the other node, rolled back and
restarted (of course application support required on the "client"
side). It's not perfect, but most of the time. We had only a few total
crashes, but mainly due to storage issues, but also due to some bugs
in the cluster stack.

Nevertheless, it's very good to see that a simple third vote solution
is on the horizon, which could be easily integrated in a RPi or an
even less "powerhungry" machine.

Best,
Andreas

On Wed, Sep 28, 2016 at 3:46 PM, Thomas Lamprecht
<t.lamprecht at proxmox.com> wrote:
> Hi,
>
> QDisks are not ideal and those itself will probably not supported by Proxmox
> VE, also I would really love top see the term "two node HA" vanish, as its
> only marketing talk and is technically simply not possible (sadly basic
> rules of our universe make it impossible), they call a setup with three
> voters (the two nodes + the storage node) two node HA to sound better...
>
> That said, rant aside, there are plans to add the corosync (our cluster
> communication stack) QDevice daemon which allows then qdevices (at the
> moment there is only QNetd) to provide votes for one or more cluster.
>
> This QNetd device may run on a non Proxmox VE node and uses TCP/IP to
> communicate with the cluster.
>
> So you can have a two node cluster, setup the qdevice daemon there and the
> qnetd daemon on your storage box which then provides the third vote needed
> to allow recovery on a failure of one of the two Proxmox VE nodes.
>
> Patches for this are already on the list, whats mainly missing is -
> obviously - reviewing them and documentation of this all (which I'm doing
> atm).
>
> cheers,
> Thomas
>
>
>
> On 09/28/2016 03:26 PM, Andreas Steinel wrote:
>>
>> Hi,
>>
>> I'd like to ask if there are any plans to use e.g. the shared storage
>> as a quorum/voting disk like the oracle grid infrastructure uses it to
>> get a two node ha cluster (for almost a decade). This obviously only
>> works for NAS or SAN storage.
>>
>> Best,
>> Andreas
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>
>
>
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