On 2015-01-16T08:11:48, Ulrich Windl <ulrich.wi...@rz.uni-regensburg.de> wrote:
> Hi!
>
> MHO: The correct time to wait is in an interval bounded by these two values:
> 1: An I/O delay that may occur during normal operation that is never allowed
> to trigger fencing
> 2: The maximum value to are willing to accept to wait for fencing to occur
>
> Many people thing making 1 close to zero and 2 as small as possible is the
> best solution.
>
> But imagine one of your SBD disks has some read problem, and the operation
> has be be retried a few times. Or think about "online" upgrading your disk
> firmware, etc.: Usually I/Os are stopped for a short time (typically less
> than one minute).
Newer versions of SBD are less affected by this (and by newer, I mean
"about 2 years ago"). sbd uses async IO and every IO request is timed
out individually; so IO no longer "gets stuck". As long as one read gets
through within the watchdog period, you're going to be OK.
In addition to that, I'd strongly recommend enabling the pacemaker
integration, which (since it was new functionality) couldn't be
auto-enabled on SLE HA 11, but is standard on SLE HA 12. On SLE HA 11,
it needs to be enabled using the -P switch.
Then you can enjoy shorter timeouts for SBD and thus lower fail-over
latencies even on a single MPIO device.
> Unfortunately the SBD syntax is a real mess, and there is not manual page
> (AFAIK) for SBD.
... because "man sbd" isn't obvious enough, I guess. ;-)
> YOu can change the SBD parameters (on disk) online, but to be
> effective, the SBD daemon has to be restarted.
Yes. Online change of parameters is not supported. You specify them at
create time, not all of them can be overridden by commandline arguments.
You should not need to tune them in newer versions.
Regards,
Lars
--
Architect Storage/HA
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Jennifer Guild, Dilip
Upmanyu, Graham Norton, HRB 21284 (AG Nürnberg)
"Experience is the name everyone gives to their mistakes." -- Oscar Wilde
_______________________________________________
Linux-HA mailing list
Linux-HA@lists.linux-ha.org
http://lists.linux-ha.org/mailman/listinfo/linux-ha
See also: http://linux-ha.org/ReportingProblems
