[Linux-cluster] Last tuning on Quorum Disk / question

[Lon Hohberger]

On Fri, 2008-01-04 at 09:02 +0100, Alain Moulle wrote:
> Hi Lon,
> 
> Finally, I adopt this quorum disk configuration :
> 
> <quorumd interval="1" label="QDISK0" min_score="1" tko="10" votes="1">
>        <heuristic interval=2 tko="3" program="ping -t1 -c1 172.21.1.12" score=1/>
>       <heuristic interval=2 program="ping -t3 -c1 172.21.1.12" score=1/>
> </quorumd>
> 
> 
> I just wonder if the interval values for quorum disk with regard to
> the one for heuristic is the best choice or not ?

* should have quotes around attr values:
  interval=2 -> interval="2"
  score=1 -> score="1"

* -cX is the number of pings to send.  When using -c1, you should 
   use tko="3" or something similar.

* -tX is internet time to live - usually the number of router hops.  
  For a local gateway, X should be 1.

> And which are the rules to fit the good value for interval and tko
> on heuristic ? (I don't completely understand why your both heuristics
> avoids suicide if one ping get lots, it seems to be due to tko value
> but ... )

1.  <heuristic interval="2" tko="3" program="ping -t1 -c1 172.21.1.12"
score="1"/>

"Send one ping 172.21.1.12 one time with a max IP TTL of 1.  Do this
every 2 seconds.  If this execution fails 3 times, we're done."

2.  <heuristic interval="2" program="ping -t1 -c1 172.21.1.12"
score="1"/>

"Ping 172.21.1.12 one time.  Do this every 2 seconds.  If we fail to get
a response from this operation, we're done."

3.  <heuristic interval="2" program="ping -t1 -c3 172.21.1.12"
score="1"/>

"Send 3 pings to 172.21.1.12.  Do this every 2 seconds.  If we fail to
get a response from this operation, we are done."


... 1 and 3 are almost equivalent: 3 ping packets must be lost to decide
the heuristic is dead.

... 2, however, means that if the ping packet is /ever/ lost, the
heuristic is dead.

-- Lon