[ClusterLabs] SBD & Failed Peer

Jorge Fábregas jorge.fabregas at gmail.com
Sun Sep 6 21:28:21 EDT 2015

On 09/06/2015 04:23 PM, Jorge Fábregas wrote:
> Assume an active/active cluster using OCFS2 and SBD with shared storage.
> Then one node explodes (the hardware watchdog is gone as well
> obviously).  

Ok I did two tests with this setup on my KVM lab  (one with SBD with
shared-storage and the other with hypervisor-based STONITH
(external/libvirt) while actively writing to an ocfs2 filesystem.

## SBD with shared-storage

Shut off one node abruptly (VM power-off) . Result: DLM/OCFS2 blocked
for about 30 to 40 seconds and then it resumed.  That's nice!  I think
at this moment (when resuming) the assumptions were:

 -if the peer were alive it would have swallowed the poison pill we just
- if the peer is freezed the watchdog would have taken care of him
- we just wait a little extra bit before continuing...

(I really don't know if checking when was the last update of your
partner - on the SBD disk-  is part of the role of the SBD daemon)

## External/Libvirt

I shut off one node but then disabled SSH on KVM host (so that fencing
via qemu+ssh couldn't work).  Result: it blocked FOREVER.

Am I right in thinking that SBD is the way to go when using OCFS2
filesystems?  (compared to hypervisor-based fencing or management-boards
like iLO, DRAC etc)?

Now, the only thing I don't like about SBD is that when it loses contact
with the shared disk, both nodes commit suicide.  I found out there's
the "-P" option to SBD (that's supposed to prevent that as long as
there's cluster communication) but it doesn't work in my SLES 11 SP4
setup.  Maybe it's on SLES 12.


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