[Lustre-discuss] Implementing MMP correctly

[Jim Garlick]

On Tue, Dec 22, 2009 at 02:12:44PM +0100, Michael Schwartzkopff wrote:
> Hi,
> 
> I am trying to understand howto implement MMP correctly into a lustre failover 
> cluster.
> 
> As far as I understood the MMP protects the same filesystem beeing mounted by 
> different nodes (OSS) of a failover cluster. So far so good.
> 
> If a node was shut down uncleanly it still will occupy its filesystems by MMP 
> and thus preventing the clean failover to an other node. 

Hi, ldiskfs (or e2fsck) will poll the MMP block to see if the other side
is still updating it before starting.  If updates have ceased, the mount
or fsck will start.  So the workarounds below are unnecessary.

> Now I want to 
> implement a clean failover into the Filesystem Resource Agent of pacemaker. Is 
> there a good way to solve the problem with MMP? Possible sotutions are:
> 
> - Disable the MMP feature in a cluster at all, since the resource manager 
> takes care that the same resource is only mounted once in the cluster
> 
> - Do a "tunefs -O ^mmp <device>" and a "tunefs -O mmp <device>" before every 
> mounting of a resource?

tune2fs -Eclear-mmp is a faster alternative.

Should only be necessary if e2fsck is interrupted.
(e2fsck does not regularly update the MMP block like the file system does)

> - Do a "sleep 10" before mounting a resource? But the manual says "the file 
> system mount require additional time if the file system was not cleanly 
> unmounted."
> 
> - Check if the file system is in use by another OSS through MMP and wait a 
> litte bit longer? How do I do this?
> 
> Please mail me any ideas. Thanks.
> 
> -- 
> Dr. Michael Schwartzkopff
> MultiNET Services GmbH
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