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List:       linux-ha-dev
Subject:    Re: [Linux-ha-dev] Re: [Bug 132] Heartbeat requires all nodes to
From:       Lars Marowsky-Bree <lmb () suse ! de>
Date:       2005-08-19 9:16:36
Message-ID: 20050819091636.GI13344 () marowsky-bree ! de
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On 2005-08-18T16:47:18, Alan Robertson <alanr@unix.sh> wrote:

> >The same RA, or one very close to it, then also should be able to handle
> >OCFSv2, as it happens.
> >
> >(GFS's DLM requires the ability to fail pre-notifications apparently,
> >but that can be worked around.)
> 
> Since our membership algorithm computes membership in well under a 
> second, and noticing that membership needs to be recomputed takes a good 
> fraction of a second (up to many seconds), sending a "we're going to 
> recompute membership - hold off now" seems a bit silly.  But, I know 
> perfectly well that's not your problem.

I didn't say they require pre-notification from the membership layer;
this refers to the pre-notification when we're about to do something to
one of the clones.

The cycle works like this: 

- Pre-notify DLM (which suspends it);
- reconfigure on all nodes;
- tell all nodes to go on (resume).

This doesn't involve the membership layer in any way except as an input
to the CRM.

> And, this is in addition to the RA work for the filesystem itself.  So, 
> it may be some more than an RA (which I think we already knew).

Well, it could potentially benefit from bugzilla #99 being implemented,
but that would be an optimization only.

Tieing the DLM to our membership layer directly wouldn't work well; they
require the membership events they get to be post-fencing, and
membership is on a per-namespace level. This maps perfectly to a
clone-aware RA.


Sincerely,
    Lars Marowsky-Brée <lmb@suse.de>

-- 
High Availability & Clustering
SUSE Labs, Research and Development
SUSE LINUX Products GmbH - A Novell Business	 -- Charles Darwin
"Ignorance more frequently begets confidence than does knowledge"

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