[Linux-ha-dev] moving quorum

[Alan Robertson]

Dejan Muhamedagic wrote:
> On Thu, Sep 14, 2006 at 05:50:10PM -0500, Serge Dubrouski wrote:
>> On 9/14/06, Dejan Muhamedagic <dejanmm at fastmail.fm> wrote:
>>> On Thu, Sep 14, 2006 at 09:14:17PM +0800, Huang Zhen wrote:
>>>> Command "hb_delnode" may help in this situation.
>>> yes, it does. then one must hb_addnode afterwards. i can't see any
>>> (obvious) reason why the cluster itself couldn't handle this
>>> automatically.
>> Wouldn't it break the whole idea of quorum? Imagine 3 nodes cluster in
>> case of split brain. There will be 2 parts with one node and with 2
>> nodes for example. Both parts are up but can't communicate to each
>> other. Both will decrease quorum by one and it'll allow both of them
>> to acquire quorum back.
> 
> the idea was that the partition which has quorum reduces the
> number of members. the new number of nodes should be used to make
> future quorum calculations. the partition which is without quorum
> shouldn't, and need not, use this. once the split brain is
> rectified, the partition which has quorum may allow the minority
> to join the majority seamlessly and set the new number of active
> nodes.

I can certainly see an argument for this -- but this isn't the way it
works ;-).

The reason why we chose (and it was a choice) to require hb_addnode
afterwards was to keep someone from accidentally rebooting the node back
into the cluster when it had, in truth, been removed.

My general thought was that avoiding administrative errors is a high
priority.


-- 
    Alan Robertson <alanr at unix.sh>

"Openness is the foundation and preservative of friendship...  Let me
claim from you at all times your undisguised opinions." - William
Wilberforce