> 9 авг. 2019 г., в 9:25, Jan Friesse <jfrie...@redhat.com> написал(а):
> Please do not set dpd_interval that high. dpd_interval on qnetd side is not 
> about how often is the ping is sent. Could you please retry your test with 
> dpd_interval=1000? I'm pretty sure it will work then.
> 
> Honza

Yep. As far as I undestand dpd_interval of qnetd, timeout and sync_timeout of 
qdevice is somehow linked. By default they are dpd_interval=10, timeout=10, 
sync_timeout=30. And you advised to change them proportionally.

https://github.com/ClusterLabs/sbd/pull/76#issuecomment-486952369

But mechanic how they are depend on each other is mysterious and is not 
documented.

I rechecked test with 20-60 combination. I get the same problem on 16th failure 
simultation. The qnetd return vote exactly in the same second, when qdevice 
expects, but slightly less. So the node lost quorum, got vote slightly later, 
but don't get quorum may be due to 'wait for all' option.

I retried the default 10-30 combination. I got the same problem on the first 
failure simulation. Qnetd send vote after 1 second, then expected.

Combination is 1-3 (dpd_interval=1, timeout=1, sync_timeout=3). The same 
problem on 11th failore simulation. The qnetd return vote exactly in the same 
second, when qdevice expects, but slightly less. So the node lost quorum, got 
vote slightly later, but don't get quorum may be due to 'wait for all' option. 
And node is watchdoged later due to lack of quorum.

So, my conclusions:

1. IMHO may be this bug depend not on absolute value of dpd_interval, on 
proportion between dpd_interval of qnetd and timeout, sync_timeout of qdevice. 
Because this options, I can not predict how to change them to work around this 
behaviour.
2. IMHO "wait for all" also bugged. According on documentation it must fire 
only on the start of cluster, but looked like it fire every time when quorum 
(or all votes) is lost.
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