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Re: [linux-lvm] Cluster LVM



On Wed, Feb 27, 2002 at 10:19:49AM -0700, Andreas Dilger wrote:
> On Feb 27, 2002  12:45 +0100, Remco Post wrote:
> > clusters all have one major problem to solve: split brain. Make sure that the 
> > node manipulating the LV/VG does indeed have the right to do so, and doesn't 
> > screw up everything for everybody. Maybe introduce a (LV/VG) master concept 
> > into the VG, so as long as that is set, no other node in the cluster will 
> > manipulate anything in the vg. (just some random rant, ignore if I'm talking 
> > nonsense ;)
> 
> Having a single master is a _terrible_ idea, since this would mean that
> if that node is down you are unable to change the VG until/if it is back
> working again.

The VG being locked is not _that_ terrible - after all - you only need
this to change your storage configuration (I don't expet the LVM to
actually lock access to the device).

> Rather use a DLM (as the other poster suggested) and a client needs to
> get a lock on the VG in order to change anything.  You can start with
> a lock per VG and one per shared PV not in a VG, and then go more fine
> grained if you want (e.g. write lock on VG and specific LV being changed,
> which does not block users of other LVs).  In the end, because you are
> not changing a VG configuration very often, and it doesn't take very long
> when you do (excluding pvmove), the big lock is probably enough.

Alternatively one could implement the cluster LVM as a simple
"resource", and leave it to the resource manager to do locking and
STONITH. The ocf (Open Cluster Framework) or "linux-ha" lists would be
good places to query for more information.



-- 
Ragnar Kjørstad
Big Storage



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