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Re: [Linux-Cluster] Submitting two new resource plugins to the project



On Monday 01 June 2009 21:17:30 Rafael Micó Miranda wrote:
> Hi,
>
> I have developed a couple of resources for Linux-Cluster (CMAN
> +rgmanager) which try to fix some needs I see in Linux-Cluster when
> compared with other cluster solution (concretely, Linux-HA a.k.a.
> Heartbeat). I am a Linux-HA user and I think this two functionalities
> could be useful in Linux-Cluster.
>
> I would like to give them (both resources) to the community to make them
> be into the project, and maybe after testing/quality testing or so be
> included into the RedHat Enterprise Linux packages of Linux-Cluster, so
> RedHat will give support for them and include them into the
> system-config-cluster tool to have a GUI that can configure this
> resources and handle their information.
>
> I'll give you some details of both resources:
[...]
>
> 2.- lvm-cluster: tries to bring to Linux-Cluster an exclusive shared
> storage option, using features of LVM2. I got accustomed to this kind of
> volumes when working with Linux-Ha + EVMS solution (using Cluster
> Segment Manager plug-in).
>
> When defining a new LVM2 volume four your cluster, you can set it as
> cluster-disabled (the volume will behave as a local volume even if it is
> on shared storage) or as cluster-enabled (the LVM volume can be
> activated on many different cluster nodes at the same time).
>
> Of course, if the filesystem placed into the LVM volume is not a
> clustered filesystem (GFS2) a cluster-enabled volume allows a bad
> administrator mount a no-clustered filesystem (EXT3) in more than one
> node of the cluster which may produce filesystem corruption. This is
> because the LVM "open flag" of the filesystem is not propagated through
> all the members of the cluster, so there is no knowledge of the state of
> the filesystem and this situations can happen.
>
> This can be fixed with some of the options of LVM, specifically the
> "enable exclusively flag". This flag, when used over a cluster-enabled
> volume, will allow the VolumeGroup to be imported by all the nodes of
> the cluster but the LogicalVolumes into the VolumeGroup can only be
> activated by a single node. So, only one node of your cluster will have
> the LogicalVolume device (for example /dev/VolGrp01/LogVol01) and the
> problem explained above cannot happen. This is not about propagating the
> "open flag" through the nodes, this is about making the LogicalVolume be
> in only one node.
>
> I have developed lvm-cluster as a resource to be used into a service of
> your cluster. In the arguments you an specify the name of the
> VolumeGroup and the LogicalVolume to handle.
[...]

This looks very useful. We are using a shared storage with CLVM, and a non-
clustered FS. I always fear mounting the same FS on different nodes. I have 
always hoped this feature could exist the LVM layer.

It would be great to see this incorporated in CLVM.

-- 
Xavier Montagutelli                      Tel : +33 (0)5 55 45 77 20
Service Commun Informatique              Fax : +33 (0)5 55 45 75 95
Universite de Limoges
123, avenue Albert Thomas
87060 Limoges cedex



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