[DRBD-user] speed of fail-over..

Stefan Seifert nine at detonation.org
Fri Oct 17 23:10:13 CEST 2008


On Friday, 17. October 2008, Little, Kevin wrote:
> I searched the archives for this, but found nothing.
>
> I've seen mentioned
> (http://fghaas.wordpress.com/2007/06/26/when-not-to-use-drbd/) that the
> fail-over time for DRBD+Heartbeat is on the order of 20 seconds.
>
> First, is this accurate?

The number highly depends on your setup and the applications you're running. 
As such it cannot be accurate. What it does show is the order of magnitude 
you can expect. Depending on your setup it can also be two seconds or even a 
minute.

> Second, what portion of the 20 seconds is a 
> function of Heartbeat, what portion is a function of DRBD?

DRBD itself depends just on your ping-int and ping-timeout and maybe the 
timeout value. You can tune them to your system and can even get down to 
about one second of fail over time. But don't overdo it. If your system is 
just under very high stress and answers late, you may push it to a fail over 
at a time, where it's not needed and possibly the worst timing. Be sensible.

In my experience most of the time is not used for detecting the fail over 
condition, but simply for starting services on the stand by node. This could 
be minimized if the applications can cope with getting their data files at 
runtime and thus can be started at system boot.

Regards,
Stefan



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