- **summary**: fm: Split-brain avoidance in OpenSAF using fencing --> fm: Add
support for STONITH fencing
- **Milestone**: 4.7.2 --> 5.1.FC
- **Comment**:
As per the description of the ticket, the idea is to use STONITH for fencing.
Just as a note - there are multiple other tickets around the topic of
additional hooks in OpenSAF for fencing like for eg:- 441, 769.
However this topic of fencing needs a wholistic approach and based on past
discussions from the FM/CLM maintainer and the TLC and architectural
discussions - tickets 79, 439, 1170 have come to exist. Once 439 comes into
place the action of fencing nodes would have to be done in CLMNA.
Having said that, this ticket as it stands today i.e. as per 5.0 architecture,
FM is perhaps the right place to provide this additional hooks for fencing
using STONITH. (And of course this responsibility would move from FM to CLM
later).
Also, changing the slogan of the topic based on the description provided.
---
** [tickets:#1859] fm: Add support for STONITH fencing**
**Status:** assigned
**Milestone:** 5.1.FC
**Created:** Wed Jun 01, 2016 01:49 PM UTC by Hans Nordebäck
**Last Updated:** Wed Jun 01, 2016 02:14 PM UTC
**Owner:** Hans Nordebäck
Split brain can occur in OpenSAF if either both links between the two
controllers are "lost"
or one of the controller "live hangs".
OpenSAF handles and detects split-brain via FM and uses PLM to fence the other
system controller using reboot. PLM only supports target environments running
on particular hardware
Only a few split-brain cases has been seen and only when running in virtualized
environments:
1) Virtual switches problems that makes SCs isolated from each other.
2) Both TIPC links between the SCs are "down/lost", e.g. TIPC tolerance time
too low, non-redundant links, other latencies etc.
3) A system controller in a virtual machine is "live hanging" for several
seconds, e.g. due to
live migration/snapshotting.
To be able to do power fencing in a virtualized environment this ticket suggests
to use STONITH.
When FM detects its peer is not available, both active and standby, in an
virtualized environment the active FM system controller will use STONITH to
power fence the FM standby system controller, (not power reset). The FM standby
system controller will also power fence, but with a delay, the active FM
system controller.
This will solve the above identified split-brain cases.
It will also fit well with the roaming feature. E.g. after power fencing a
standby controller a new standby controller will automatically be selected by
the roaming feature.
---
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