Hi all,
I'm thinking about to implement SBD as resource agent to support clone mode.
However, it turns out to be problematic after comparison. I'd prefer
to stay with current SFEX implementation and only make SCSI-3 support
clone mode.
May I have your comments on my analysis ?
==================> Start here <=======================
As we known, both SFEX and SBD implement cooperative protocols between nodes.
The difference is that SFEX implements the exclusive mode, while the
SBD implements the shared mode.
Think about sfex's exclusive mode.
node A | node B
|
Rsc_SFEX |
^ |
| |
Rsc_Fs |
When split-site happens, as long as we prohibit the starting of
Rsc_SFEX on node B, Rsc_FS won't start there either due to the
dependency rule.
Then think about SBD's shared mode.
node A | node B
|
Rsc_SBD:1 | Rsc_SBD:2
^ | ^
| | |
Rsc_Fs:1 | Rsc_Fs:2
When split-site happens, what we really want in the first place, is
to stop Rsc_Fs:2 as soon as possible. However, preempting Rsc_SBD:2
doesn't ensure the stopping of Rsc_Fs:2, because it's only a
cooperative protocol on the storage.
Possible solutions are:
1) suicide the whole node. But hey, then what's the difference to a STONITH ?
or 2) upcall to Rsc_Fs to kill it. Sounds worse.
====================> Finish Here <===================================
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